Ok update to the saga.
Guy is still multi-dating (some chicks have common points with him, some have very little but look good). I have taken my distances. After he still tried to talk to me while showing up with his girl of the month, I got mad and told him to stop communicating. He got really mad (insecure guy I guess) and blocked me on social media (we were not in each other's contacts so big deal).
I made it clear that I disapproved off this girl, while being friendly with the ones who have substance if I had a personal interest in them (cultural, work). He brings some of them to our social circle.

Anyway, now he's becoming aggressive towards me. I tried to be civil and while I don't wish to play friends, I think it's ok to say "Hi, how are you? Good? Great. Bye". We have common friends and it's very awkward to be in a group and to feel that ice build up.

Yes, he probably heard that I disapprove of his lifestyle but surely that's not news. So why on earth is he so mad at me.
In the past he was mad because I "prevented" him from living his multi-dating or low quality dating life (with women he had very little in common with but who admired him endlessly).
Is it still that??? But I don't talk to him beyond "Hi, how are you? Good? Nice."

I know it shouldn't preoccupy me but it's hard when you have so many common friends and they start to find this frosty communication or ignoring entertaining or annoying.
I can't avoid him entirely without giving up my places and activities I am attached to.

A friend said that he sees professional competition in me (could be). Another that he doesn't know what he wants (probably). Another that I shouldn't waste a thought about it (I am not a robot. We can't avoid each other constantly), another friend close to him that I should date (I am) and not be needy (I told him that to someone who for some reason doesn't want u around "hi" is already needy. Perspective, perspective).

I am pretty sure he trash talks me to people (to convince himself that I am awful?).
Some people start acting weird with me. Some are hostile (his ex), some avoid me (staring at me and not greeting me), some have become over-friendly.

What do you recommend? Talking to people seems to be pointless as they just pretend nothing is wrong and I am tired of being told that I overthink, that I'm needy etc...

I just want "normal" relationships with people. If they don't like me, fine, go away.
But why this circus?