My advice to you would be to honestly not worry about being 25 and still single.
I'm 28 and still single! Well, recently single.
My only real relationship finally happened when i was 27 years old. Previously, like you, i'd had some intimate experience with others, but not much. By nature i'm quite a reserved, traditional person so it was never my intention to become too intimate with another person until i was in a relationship that was going somewhere serious. Thats polite talk for saying i'm a bit of a prude, lol.
The fact that i'm relatively a late starter compared to most people out there never concerned me. I wanted to wait til the the right person and right moment.
As for you being diagnosed with BP, i don't see that ever preventing a good man from loving you for who you are. My mother is BP and she's been in a decent relationship for over 10 years now. Previous to that she was with my father for almost 20 years (and it failed in the end because of his behaviour). If someone loves you for the special person you are then they'll learn to adapt to these things so they can share their life together with you.
As for finding it challenging to sustain a conversation with men you like, i'm not a brilliant conversationalist myself yet i manage to get by! In fact i'm pretty boring.
My advice is just to do what i do - encourage the other person to talk about themselves! People love to talk about themselves!
If you patiently listen and show interest, they'll appreciate it. I may not be a dazzling conversationalist, but people (particularly ladies) seem to appreciate me because i'm a good listener.