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.

outlasting humanity and all its trappings

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?”

Repeated surgical corrections for your ever growing earlobes

If everyone gets to be immortal, imagine never being able to get rid of dictators. Putin’s 600th won election.

People in the future wouldn’t be allowed to have children, Earth will be filled to the brim with very old people and very few new ideas.