I essentially agree with finally-free and sweet tea. I would like to add that while I feel like I could never cheat on my girl, Darwinian baggage sometimes has our genes telling us that to do otherwise when the chemical synapses in our brains start firing cause it just feels so damned good and exciting to be with someone new, and even to be "bad", I have in the past maintained friendships with men who casually cheated on their significant others. Why? Cause I valued their friendship to me. But honestly they are/were calculating, cold-blooded bastards.
I guess all I can say to you is, contemporary morality seems to be swayed towards "if you do have sex with him/her, be protected against disease." I can't argue against that model, but we're hard-wired and then "enlightenedly" programmed by the last few hundred years of "progressive" society for a lot more consequences than that. I think there would always exist an element of distrust, maybe jealousy, between you and he, and I couldn't live with that in a monogamous romantic relationship. Neither could B.B. King or his first wife, it's what killed their marriage.