Should i tell him i like him again?

Maybe you need to slow down a little and hit the brakes. It's understandable about how you feel about him, but it's just not that great of an idea. Your hunches are correct about not telling him because he has a girlfriend. And because of that, it would be best to keep it to yourself. Don't get in there and distrupt whats going on between them, and don't listen to your friends, either. Keep your relationship with him as a friend and that's it - period. If he should break up with his girlfriend in the future, then yeah, go for it. But now, even if he's giving you signs that he's interested, just leave it alone.