People have various opinions about having sex with an estranged spouse. All I will say is that if you are doing it strictly because you don't want to lose him then perhaps you shouldn't be doing it. Also, I am sure you are smart about this but I hope you are using protection, especially if he could be sleeping with the OW.
I'm pretty new here myself so I apologize I don't have as much advice as some of the vets on this board do.
"Everyone you meet has baggage. Find someone who loves you enough to help you unpack." ¤Formerly DelinquentGurl¤