First and foremost, if it isn't destroying your life, then you don't have a problem at all, if it get's in the way immensely of your survival and happiness then you've got a problem.
Isolating one self isn't really a symptom of anything really, neither is suicidal tendencies, who wants to hang out with them anyway, not to mention suicidal thoughts creep into everyone of our lives. Especially when you get older, it's just a part of our lives, some just do it sooner that's all.
And all of the happy ones, or as some call it ignorant, think your the weird one, but slow and steady wins the race.
I would suggest in your case to study some type of art that you really enjoy and can't get enough of. The isolated when disciplined can accomplish great things, so get busy and make your life better.
Not wanting to stay in a relationship is not a symptom of anything, who cares about that, there are plenty of people doing that, not everyone has to do that or even want to.
It's possible that you may have something, but you only need to be prepared if something does go wrong, not worry about it all of the time, trust me if you had a psychosis you'd probably be in a hospital right now.
If you are worried about it then look up the signs of an actual psychosis and then if you have one then go to the hospital, that's it, that's all that there is to it.
If you are then you are, if you aren't then you aren't, no need to mill over it all of the time, and stop being so critical about yourself.