All the people trying to dissect you for science.

Idk id be super depressed if I was able to experience my family, friends, family's children, and so on die.

outlasting humanity and all its trappings

i think that experiencing all the things & people i care about would be the worst of it.

either that or seeing us repeat history over and over again as a society complete with all of the indifferent cruelties it entails and studying it, but ignoring it anyways

As OP mentioned, a lot of replies focus on loss, that friends will inevitably die and objects will break........ we already face that reality with regular life! That's hardly a downside of immortality itself.

Everyone else in your life that isn't immoral (if you're the only one who is) dies eventually, so every time you make a friend or start a family, you do so knowing that you will have to watch them all die someday.