ok what in the actual fuck??

ok so i broke up with my ex like 2 Octobers ago, and she was talking to somebody while we were fucking dating and went to them immediately after we broke up, and also she got all touchy feely with my best friend  pre-breakup, and now she GOT WITH MY SISTER WHILE SHE WAS WITH THE OTHER PERSON like WHAT and my friend lets call her "Cory", anyway Cory told the other person my ex was getting with my sister, my ex didn't even breakup with the other person before going to my sister and like that's literally kind of fucked up, listen i get that she got over me real fast idrc, but when you don't breakup with the other person before going to my SISTER, and Cory has to tell them, that's where I kind of think its a little weird, mind you my ex and the other persons relationship was online the other two are in real life, like she goes to my school. and yes i am happy for my sister, i am happy she got a girlfriend but shes dating my ex, surely that breaks some kind of girl code or bro code whatever. anyway i just accepted it, like last week, (when they started dating) but if my ex cheats on my sister, i am cutting my ex out of my life, (we stayed friends post-breakup)