Then just do something else instead that you want to do.
It seems to me that either:
You made this game a part of your identity / are defining yourself over this game, thus it's hard to not play it because maybe you have ambitions to get good etc.
or you're really just addicted to that feel of doing well / gaining score / pp and there's nothing else like it (yet) that could get you equally motivated because, I assume, you're not really good at other skills or hobbies, probably don't have any to begin with so it's hard to get motivated to do something else.
and / or you really just don't have anything else to do so you just find yourself going back to osu! simply because you feel there's nothing else to do.
Honestly you don't really have to quit osu! as much as you just have to find something else in life that's productive. That way you won't get the crippling depressive thoughts you probably have when you go to bed, thinking that you, again, didn't do anything this day while life flies by.
You don't really have to necessarily go out and meet people and all that stuff. It's very hard, impossible rather to tell if you really want to do all that stuff you say you want to do or if you just feel forced to do it because that's what society depicts as a good, desirable life.
I don't want to digress into some kind of psychoanalysis, so I'd say you just need to find something to do that you want to do but is also productive.
Maybe you don't really know what you want to do or what you like to do because you never tried and never took the time to think about yourself (which is perfectly normal, no worries)
Maybe you want to get into editing, drawing or music or whatever. If so, then I'd just start doing that. Also, don't try to force yourself into something like that with a mindset where you try to work at that stuff for the same time you played osu.
Just try to do something productive / something that gets you closer to what you eventually want to do in life and you won't have to feel bad about playing a game that you like. Nor will osu feel that important to you anymore in a way that would make it hard for you to quit.
If you go to school / have a job I'd also not worry about playing osu! all day. I mean, if you're going to school you're doing something productive, if you have a job you're doing something productive already.
Again, you know yourself better than I do but you'll probably recognize yourself somewhere in these lines.
TL;DR
Find a hobby and build the habit of working on your hobby / job / school everyday so you won't feel bad about not doing anything in your life.
You don't have to be some kind of super-social guy, being outside 24/7 all day etc etc. Live your own life dude