Opinions?

I wanna start off by saying I'm Demi aroace and I'm kinda dense so just be aware of that? Also I'm hella scared to post anywhere so please don't hate me!!! :(

I wanna ask if ANYONE knows what to do in a situation where your ex (first bf) wants to date again. I got back with him once and that's cause he broke up with me because he was getting stressed. The second time he broke up with me he had some serious mental insatiablity and thought I was "attacking" him when I got slightly upset over a misunderstanding. The whole things been stressing the shit out of me and I just need guidance.

Not to mention his bestfriend had a crush on me all throughout this then tried getting with me NOT EVEN A DAY AND A HALF after we broke up and like now he has a gf? He started dating her a day after I rejected him