The best guideline I can give anyone on this forum is this :
If your spouse is cheating on you, and they ask for something.. Don't give it to them.
I don't recall how much exposure you have running on this or how much guilt he's feeling, but right now him coming back ins't a good thing anyways... If he came back I would tell you to reject him anyways... He's got a talent for talking and then running a few days later when the pressure kicks in...
That will be to your advantage when he leaves to meet OW... the pressure will kick in there too... He has a family with you and his baby and he will most likley run THERE FIRST...
YOU need to get yourself strong enough to tell him NO... NOT until you GROW UP