How can I help my ex when the baby his girlfriend is carrying isn't his?

alright… I've been thinkin about this question I need answered lately. I can't seem to answer this by myself… well my ex. boyfriend and I broke up like 6 months ago.. we went out for only 4 months off and on.. he was my friend for about a year and a half before he started going out.. we broke up off an on b\c I cheated on him.. but he still kept on giving me chances.. I took adventage of them.. and I never really knew how much he really loved me.. now he has a g\f… and shes pregent????!!!! I freaked out when I found out.it hurt so bad when I found out. but he still asks about me.. and everyone knows he misses me.. we've been through a lot together.. and when I see him I can't talk to him or even look at him in his eyes. but the baby shes carryin might not be even his.. and he knows it might not be his.. b\c when she found out she was pregent.. she was now 7 months pregent.. and we broke up 6 months ago… what if he finds out if its not his??? what do I do??? I still care about him a lot… I regret everything I have done. an now that I know he really did love me.. I want to be there if its not his.. I can tell hes depressed.. him and his g\f fight all the time and he has gained a lot of weight since we broke up… what should I do?? I can't just sit back and watch him be like this??