Asklemmy

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.

Based on your question, you might dig the book “Boat of a Million Years.” The author put quite a bit of thought into just that.

https://en.m.wikipedia.org/wiki/The_Boat_of_a_Million_Years

Getting imprisoned for thousands of years unable to get out.

The disappointment of experience winning lifetime supply of something but that would eventually turn into a lie

If other people are also immortal, the awkwardness of all of them eventually becoming your exes

Just depression in general. I don't want to live one lifetime, let alone never being able to die.

If you're immortal in a body that isn't broken then that might be a different story, but you'd still grow to love people only to have to lose them and go through that pain over and over.

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.

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.

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?"

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.

Friends, family, and lovers dying before you.

Having to listen to that Queen song, forever.

On one hand, you have eternity to come to grips with everything you've done. On the other hand, it might take eternity to come to grips with everything you've done.

Seeing all of your friends and family die, knowing you'll never stop missing them.

Having the perspective of centuries. Seeing society make the same mistakes over and over again because they forget, but you never do. It would drive me mad. Already does, considering I have the ability to, and have, read history. I just imagine living it over and over to be tedious.

Family meals that take 3 restaurants No retirement

Forgetfulness. Think how forgetful people get after having lived a normal lifespan, now go for a few thousand+ years and you’ve probably forgotten whole centuries of your life. This is actually the premise of a solo journaling game Thousand Year Old Vampire, you have to cross out and forget memories as you progress through the game, just forgetting whole parts of your life.

I don’t think you’d remember a break up from hundreds of years ago, let alone be upset about it.

Being eaten by sea anemones, tuna, sharks, swordfish, sea turtles, penguins, and other jellyfish.

https://en.wikipedia.org/wiki/Turritopsis_dohrnii#Predation

Btw if you were actually immortal, after a while you would just go into shock and enter a vegetative state from all the psychological stress.

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.

I suppose it depends on the rules of this specfic immortality. As someone who lives with chronic pain that literally never feels physically comfortable in any position, immortality sounds like a cruel joke. Not that I'm suicidal or eager to die, but the fact that it would progressively get worse and worse without any sort of end is.... horrorific.

Not being able to kill yourself.

One of my books features an immortal protagonist and I've as such thought about this quite a bit. More than the answers already provided here, what I found interesting as a writer was the balance I needed to find between making an immortal detached from mortal values while still being engaging to mortal readers.

Said as a pithy question, if you can outlive everyone's decisions and mistakes, what would it take to make you do anything at all?

Loneliness. I think being immortal would show someone what true Loneliness is