To Op,
Did you try when to sever ties with a friend? Also leave out BP. Ive lost lots of friends over the yrs as well. Mostly to long bouts of depression. Isolating.. just falling of the face of the planet really. When i was younger I lost friends to out of control hypomania. But looking back it was really my fault , cuz i was pretty ignorant my MI and did some crap things to good ppl. But there have been a few instances where i stopped being friends with someone purposefully. But I wouldnt describe it as "dumping or breaking up" more just realized that they were toxic and using me and just kinda cut communication. I guess unless its a really good friend that you normally talk to daily, maybe then you might feel the need to have a formal conversation about not wanting to be friends? :/ idk... IMO most ppl are pretty involved with their own stuff and dont really think much of someone fading out of their lives... IDK.