I'm sorry but you can't, it is really over. Sometimes a rebound thing turns into a relationship and this appears to be the case here.
Let him be, contacting him further is just going to annoy him and his new girlfriend, they will see you as some desperate, sad and sorry case, have some pride and self-respect. Re-focus your energy elsewhere. Concentrate on yourself and your social life, work on living life.
[SIGPIC][/SIGPIC]
Love is like a merry-go-round: you get all dizzy, and then you feel sick!