The greater part of any affair is fantasy and make-believe:

"He's a great guy, but he's trapped in an unhappy marriage. He and his wife haven't had sex in years. He says he has no feelings for her, and loves me. He feels that he can't leave because of what it would do to his kids, but I do think that he'll leave her though, when the kids are a bit older."

This is life on the edge of reality, in a little bubble of imaginings.