Having to keep creating fake identities to prevent people and governments from finding out that you're immortal. That would be a massive pain in the butt, especially in a world where mass surveillance of the population is common.

The rest of humanity will eventually evolve into something you don't recognize and can never be part of.

Repeated surgical corrections for your ever growing earlobes

If it's the realistic kind where you just don't age, the statistical certainty that you'll eventually die in an accident, or to war or murder. Your odds of getting to the heat death of the universe without making backups is pretty slim.

If it's the kind where you're indestructible, you're highly likely to encounter someone who tries to bury you alive in a subduction zone eventually, because humans are like that, and then you get to spend eternity slowly moving into the scorching mantle.

All the comments assume everybody else isn't also immortal. I forget the title and author but there's an old sci fi story (or novel?) about a future where everybody lives for centuries, and they've found that the brain only retains a certain amount of experience. They have long careers, get tired of doing whatever, re-educate and do something else, or even have multiple families they eventually forget about. A couple of the characters are surprised to find out they used to be married like a century earlier. To me that seems vaguely like reincarnation, and I kind of don't hate the idea. I really don't see any downside to that scenario, or even just going on forever.

People are focused on having regrets and negatives that last forever. But buck up li'l camper, you can learn to move on from stuff. And I say this as a dad whose daughter had cancer at age 10 (she survived). It was hell and I wouldn't want to live through that whole period again, but I don't consider it a reason not to want to live forever. The trick is to learn how to cope with these things and not let them outweigh the good experiences you have.

Sooner or later, you will get trapped somewhere forever. Over the course of an infinite lifespan, the odds that a building collapses on you or a tunnel caves in on you basically become 100%. Someday, you will fall into the hole that you will stay in until the sun explodes, and then you will drift in the void until the heat death of the universe.

Either "Boredom: After some time you have seen basically everything." or "Can't keep up: The world changes so fast, and I'm, stuck in a mindset I acquired in 1543".

And: Bureaucratic nightmare. "We have you on file as being born in 1924, but you don't really look like a centennial. Can I see your passport instead of that of your great-grandfather, please?"

How much more annoying the (much) younger generations would be.

Being asked your birthdate in order to view a game on Steam, and the year dropdown not going back far enough.

Getting trapped under something for a few thousand years.

Herpes is forever.

People are commenting 'fates worse than death' and 'being made into a labrat by the 1%', but really, if you have infinite time to just do stuff and you can't be killed -- And you don't somehow squirrel your way into a position of power then what are you even doing with your time and immortality, oomfie?

The loneliness part is also questionable. I know OP said it's overly done, but I also think it's just wrong. If you're an adult you've had people in your life die before. It sucks. You miss them. But then you move on. And you meet other people. You'll still go ":(" when you think about the person and such... But life goes on.

And that's just life. It doesn't get any worse if you extend it longer -- If anything it gets better. You might have lost your beloved today, but you have another dozen lifetimes to heal your wounds and meet someone else and fall in love again and (...)

So here's some lower-stakes, frustrating inconveniences of being immortal:

• Your favourite fashion? It's not just out of fashion. It's so out of fashion it is now considered 'historical costuming'. You can no longer find any articles like it at all. Because the only people even trying to recreate the techniques are costuming nerds and theater people who always exaggerate stuff
• You got a song stuck in your head. It is either from before recording was invented, or any recordings of it that existed are too old to be reliably listenable. You have a song stuck in your head.
• You used to really enjoy a job you did. That entire career path is now obsolete. As per the first paragraph of my post, if you're immortal you have probably snuck your way into the upper echelons of society at some point during your infinite time... But like. You're bored. You loved being a Court Jester, now there are no Court Jesters.
• Actually tedium just in general. Sooner or later you'll run out of new things to try, because you'll have done everything that even remotely caught your eye already. So what the fuck will you do with your time? You'll eventually just get depressed and not do anything.

Depends on the type of immorality. Do you continue to age? If no, what age do you stop? Eventually the universe will die. So what happens to you then?

It might be fun for a while. Maybe even a long while. But that fun will be gone in an instant compared to the trillions and trillions of years you will float in a dark dying universe of nothing.

I think you're undervaluing loneliness. Loneliness isn't just missing some one. Loneliness means there's no point in connecting with people because they will just die. Loneliness means that no one knows the depth of your condition because it isn't available to them. It means that as they change and face new obstacles, you'll be oblivious to all of that. You'll not only see them die, you'll see the vitality deep out of their pores as they age. All the while you'll never know what that means personally or feel that slow slipping.

Also, super weird that your example is a breakup and people dying is something not worth registering.

People, corporations, and other entities would over time gather more data about you. There's always some kind of information footprint that you leave behind. And you'd stand out from other humans by the way you talk (i.e. using slang from 200 years ago, and speaking about historic stuff with details that the general public is not aware of) and other traits, which makes you traceable.

You'd procrastinate things for 100s of years, until at one point you're simply no longer able to do it. Wanted to domesticate a saber-tooth cat some day? Too bad, they're extinct now. Wanted to visit the baths in ancient Rome? Well, it is not the same Rome anymore, and all the baths' floors are cold.

Basically all of the time you’re alive will be after the heat death of the universe, where you will be floating in space, with nothing to do, nothing to see, nothing to experience. Complete darkness, complete silence, in a complete vacuum, for eternity. Every other particle in the universe is forever out of your reach. You know that you will have nothing forever. You will never see, hear, or touch anything again, for all of time, which will never end. The trillions of years that preceded your float through the void fade into a distant memory as you outlive twice as much time, four times as much, a trillion-trillion times as much, and infinitely more.

immortality doesn't guarantee perpetual health, you're alive, but so broken and sick you wish you could die, but you can't

Losing all of the skills you gain. No matter how good you get at something, after a few centuries you'll have lost your edge. You can also only practice so many things concurrently without giving something up. At some point, years down the line, you might try to ride a bike again and completely fail to do it, or try to sing and fail to hit all the notes that came easily before, or do gymnastics but the muscles you need are underused. It doesn't matter that you spent years mastering every skill, your abilities will degrade over time. You'll never really be able to feel sure about your own abilities except for whatever you've done most recently.

Life will pound you into an uncaring jaded disinterested unloveable husk of a being after too many emotional scars from losing loved ones, too much of seeing humanity make the same mistakes, and too much watching the knowledge you gained turned irrelevant.

Or, life will beat into you an uncanny ability to converse and relate to others, even if fleetingly.

Watch The Man from Earth.

That old person feeling of no longer being with "it", and what's "it" now being strange and scary probably compounds over the centuries.

At some point, our sun will go supernova and you will end up drifting through space.
And all your life before that point will be less than a blink of an eye compared to the time that follows:
Trillions and trillions of years until the heat death of the universe.
And even that time will be less than the blink of an eye compared to the eternity afterwards, when you drift through a black void without any stars.

I had a really nice washing machine. Then it broke. The manufacturer was dissolved 25 years ago.

I had a really nice cast iron pan. Then it fractured. Modern cast iron pans aren't smooth.

I had a really nice car. Then a part broke. Replacement parts haven't been available for 50 years.

I had a really nice flip phone. It was made by Nokia so it still works. People think it's weird that I use a flip phone.

I had a really nice peace and quiet. Then someone invented ambulances. Now I cower in the corner of my bedroom hiding from manmade horrors beyond my comprehension.

Cancer. So much goddamn cancer. It doesn't matter what kind of immortality you have, you WILL get cancer. Repeatedly. Over and over. Forever.

Science fiction is going to age poorly. A lot of it is already hilariously dated. Look at most of Star Trek. They're flying at FTL speeds through space with artificial gravity, teleportation, lifelike androids, and replicator technology, but their screens absolutely suck. More and more of those inconsistencies are going to add up over the centuries and make things ridiculous after a while.

The number of new things that people enjoy dwindles with age. Just about everyone agrees that the music that was being made when they were teenagers is the epitome of the art. Are you going to be able to enjoy anything when you're 2563 years old?

The older you get, the faster time apparently moves. Having grown up in the 80s and 90s, on some days, even "The year 2000!!" still feels like it should be the future to me. I can't imagine what even a few centuries would do to this phenomenon, let alone a millennium or megaannum (I had to look that word up.)

On the upside, presuming I'm the only immortal, I'll be the only person currently alive to see if they actually finish that performance of Organ^2^/ASLSP in Halberstadt.

You'll be perpetually behind the times. People tend to get set in their ways even by their 30s. You'll constantly lag behind the trends, language, and tastes of the younger generation...

If you were the first to be immortal, you may not have the best version of immortality and it may render you incompatible with better, future types of immortality. Like magical regeneration that prevents you from getting a personality upload to a cyberbrain that is a million times faster and smarter than the squishy biological brain.

Wage slaving never stops

Cross the wrong people and you end up not dead, but irrecoverable. Cement shoes, buried alive kind of stuff. Cross a different set of wrong people and you become a labrat. To avoid either scenario, you'll be in a constant state of "undocumented" or false-documented which will keep you in a pretty consistent state of poverty.

Having potentially thousands of years of embarassing moments of social awkwardness to think about. And, over the aeons, being relieved when the people you know and love die because they won't remember the things you're so ashamed of.

Knowing the answer to some of history's biggest mysteries, because you were there, but being unable to speak about them because, 1, that would expose you, 2, nobody would believe you either way because nobody expects you to be THAT old.

Also, it is already frustrating seeing kids being dismissive or denying events that you yourself have lived. Imagine being thousands of years old and seeing so much shit, but those events are rarely retold, forgotten, or straight up denied by conspiracies or future governments that won't admit their fault on it.

If you have epilepsy or Parkinson's or MS, you're just going to likely get worse forever.

Discovering the upper limits to what the human mind can retain and just constantly forgetting all the shit you used to find important.