Don't mention anything to him. You need to move on, the best cure is to find someone new. Although, its nice in your head to believe that hes only got a new girlfriend as a rebound for you, so if that makes you feel better then 'tell yourself that' as they say.
But, hes clearly not told you for a reason, whatever reason that maybe. So, just take a deep breath and suck it in. He can't have both of you, and if hes saying that whilst he has this girlfriend then you can't really believe what he says.
Try not to talk to him or think about it too much.. There is always someone new and more exciting out there.