Breakup advice

My boyfriend recently broke up with me for such dumb reasons. Basically all bullshit. He has gotten into another relationship not even 2 weeks later and I’m pretty sure he was talking to her while we were dating.

And now his friend is telling me to not go and hookup with any of his mates. Isn’t that not his place?

I get it if I was the one who broke up with him, that would be dog. But HE did so can’t I hoopkuo with anyone?