guy gets jealous easily?or friends start liking each other?

I think you should try ex-girlfriend club. It has the jealousy thing you like after they got together, also they were sort of "best friends" who also sort of "dated before" lol It has a love triangle and the female lead is pretty good. i don't wanna spoil so that's all i'm gonna tell you, but i think it would be something you like according to what you asked for.