Friends relationship

So I've been friends with some girl now for over 8 years and she firstly went off with my ex, I forgave her though because I wasn't falling out with her over him! So anyway they're not together anymore and she's started dating some other guy and I know most of his ex's and he's cheated on near enough all of them, so I've told her and he's started to kick off at me and stopped her from talking to me because he's made her believe that I'm just jealous of their relationship when I've been with my partner now for over 3 years! What should I do? Thanks guys💖