If you can't stop wondering whether he's going to, whether he wants to and how you'll flame his Facebook page if he does, maybe all that energy could be better channeled. Consider a) what might make him want to do such a thing, b) why you think he might be doing such a thing and c) what you could do to avoid such a thing—affair-proofing, if you will
. In your imaginary scenario, is he looking for more sex, more fun, more attention? And in your real life, is he spending a lot of time listening to that song that goes, "As much as you accuse me of cheating, I might as well have..."? Palpate your relationship for the weak spots, think about what changes you might want to make or, here's a radical suggestion: maybe talk to him about what you're feeling.