I can't keep long term friendships and it hurts.

That's basically it. I lost all of my friends during the last six months even though I've been in behavioural therapy for three years now (20F) and I genuinely thought I was feeling better. It was a very big group and we've been knowing each other for years. We all live in the same small town and we hang out every single day. I joined the group about three years ago and I was super happy about it because I've always been a lonely child and teen. Everything is now officially over because I gradually "broke up" with each member, starting from my two best friends. I have never had a "serious" friendship: things always end up fucked somehow. I was able to break beyond repair every single friendship I had, even childhood ones. I always "fact-check" everything I do because I tend to think of myself as crazy or toxic everytime something goes wrong. My family, my therapist and my boyfriend never told me I've been cruel or unconsiderate or straight up annoying. But still, everyone leaves and I feel extremely lonely. I think I have become a decent human being but EVERY single friend I ever had abandoned me, usually because they fell in love and needed space or because of other people's trash talking. I know I'm hard to deal with (BPD, ADHD and just a weird personality in general) and I really really really put effort in getting better, but I am now feeling kind of hopeless. I feel like therapy is not worth it. Maybe I should just be grateful for my boyfriend and worry about my personal development, but I've never ever had any relationship without sexual or romantic implications and right now I feel unlovable.