That would be the worst aspect, as folk have said, losing the loved ones closest to you. Knowing that if you had kids you would definitely see them pass on, same with your partner, although , of course everyone anyway has to deal with that possibility, but generally folk do not expect to see thier kids pass on.
That would be the worst thing, because apart from that, all your mind has to cope with is the concept of everything never, ever ending.
and that would be, y'know, alright, you take each day as it comes in your mortal life anyway right? hell, the stuff that happened to me when I was 3yrs old feels as if it might as well have been 500yrs ago, so you hold onto the best memories, and the rest become just a bunch of stuff that happened.
No healthy minded person with a good life turns around when they are in the flush of their youth and says to themselves, 'holy moses, i can't be arsed going through another 50yrs of this crap, omg, what is going to happen in my future?'
It would just be the same as a mortal life in that regard, sure, you might get a panic attack once in a while , thinking, holy crap, i am going to be earth's janitor forever and there is f all i can do aboot it! but then you just sit down with your partner, friends, family, whoever, spark up a reefer and laugh about the fact you are Earth's eternal janitor. Psychologically speaking, i think that is the best way to handle it.
You would need a good healthy life, with loved ones, family friends, and that is true if you want to be truly happy in a mortal life too, but with immortality, I defo think you would need some super-powers as well as the immortality to mix things up for yourself in your spare time, to keep from going crazy with boredom.
Other folk would be filling up their jet-packs at the gas station and you could fly by and pee on their heads, stuff like that would keep you amused during your immortality.