<human>: Can you provide a brief rundown of the text in within 3 sentences?

(accidentally posted to self first)

So I became best friends with a girl in high school. She was my best friend for three years, during which time I became friends with all of her friends, basically integrated into her group. Well, about a year and a half ago we sort of realized that we had feelings for each other. We went to colleges an hour and a half apart but still made it work for a year and a half (during which time I moved in with one of her best friends form childhood).
Anyways, about a few months ago my ex cheated on me. (By the way, a word of advice: don't date your best friend, ever. When it ends, you lose so much more than just a lover.) So yeah, she cheated on me and then broke up with me.
The situation was weird because allllll of our friends were mutual (I'm living with one of her oldest friends, who is now also a good friend of mine). Anyways, I was handling it best I could. Then my ex, about a month after we break up, starts dating the kid she cheated on me with. I was devastated ("how could she move on so quickly?" etc).
Here is the problem: since my ex is friends with all of my friends, she's slowly been introducing the guy to all of them. I hate this dude with a passion for obvious reasons, but I don't really have any support, because everyone I know is friends with her and wants to be supportive of her too so they don't want to pick sides. This whole thing is killing me inside. What do I do?
(and I get the whole, "meet new people, get new friends", but it doesn't really work like that. I love my friends, it just sucks that they're also all friends with the ex.)
<bot>: dated my best friend, she cheated on me and left me for the new guy, problem is all of our friends are mutual and are meeting the new guy and can't really hate him because they want to be supportive of her as well