@violet not avpd but bpd here. I'd try to let some water pass under the bridges, by:
1- avoiding triggers (muting convos, going less social, switching to other support groups...)
2- occupying my mind until emotions decant (watch series, read books, do crafts, play videogames, sleep...)
Learning mindfulness meditation helped a bit but it's very long and there is no immediate improvement. If you have the room for it, it can be an investment to make for the long run, but I'd avoid trying it for the first time during an emotional crisis.
@violet I advice having different circles, this way you can vent into one if needed without causing a collapse of your relationships. It can be a forum, a discord server, a wow guild... whatever group you can be part of. This avoids a "all the eggs in the same basket" situations
Also, being angry is not illegitimate, it's just how you react to the emotion that can be destructive. I like to talk about the problems after my emotions settle, to address them instead of building up resentment