To each their own. Maybe he'll change, maybe he won't. It really shouldn't effect you either way, I may be reading, and interpreting your reply incorrectly, but I detected a small amount of elitism. That's fine as most people tend to believe that the way they live, is the "right" way. Or I suppose if you simply deduce it to mathematics the more partners you have, obviously the higher your chance of contracting an STD. Which if that's purely your point ignore everything else I said.
Regardless of my own opinion on interpersonal dynamics and their effects on the well-being of archetypal, generic, subjects , having a trusted friend, and partner, betray you sucks. Adding children to the mix complicates the matter further. Which begs to question the current state of family mechanics and whether or not the standard model is correct, or if some other seemingly "crazy" culture has a more efficasious approach.
I shouldn't open this can of worms. Ignore all of ^ ... TITS ARE GOOD.