What should i do.

I have to say I agree with Ken on this one, you really need to get him alone and just ask him how he feels about his ex...make sure you let him know that its okay to be honest about his feelings with you because you only want to see him happy. If he says he does still like his ex then let him know that its best that you two break up so he can sort out his feelings....he will have so much respect for you because you understood and cared enough to let him do what he needs to do. If things go well with his ex then you just gotta let it go at that...but im sure that you'll have one of the closest friends you could possibly have and that is better than nothing at all. I really wish you luck with this sweetie.

Take care, lise