Really? That's strange they always give you a different diagnosis. You do know you can have more than one diagnosis at once, right? You can have BPD and Depression at the same time. So I don't think it's farfetched to say that you might have both.
I feel you, and to be honest...you just got to look for small things to look forward to. A new game coming out...your favorite show coming on TV....your favorite Youtuber putting out a new video...coffee in the morning...things of that nature are usually what make my day more worthwhile.
Also, I saw you see little reason to go back to college. Have you tried taking online courses? They aren't too bad. You just can't forget about them though, but the work is usually not that intense. At that, it takes away the hassle of going to campus and talking to people in person.
If you have credits and no degree yet then I say you should go back. At least try taking a couple (two at most) online courses for a semester.
Wishing you luck, Richard.
Keep posting.