In love with my bestfriend

I’ve been best friends with this guy since grade 6. We’ve had the closest friendship and he started dating this girl for around two years and she was CRAZY. Controlling, manipulative, cheated on him, would get mad at him for hanging out with his guy friends or going to the gym etc but he just loved her so much. Anyway, he finally got out of the relationship a couple months ago and we’ve gotten a lot closer just flirty and stuff and we actually really like each other. I’ve never seen him so happy and all i’ve wanted was for him to be with a nice girl and i know i’d treat him amazing. I know if his ex found out she’d literally rip my head off so what do i do..? We have some classes together and we occasionally talk but she’s so crazy and i’m honestly scared of her. I don’t know what to do. i don’t want to start drama but i don’t want to just not be with him because of her