This may be something else that women don't quite grasp, but the less likely he is to leave you for her, the more likely he is to want to continue the affair. Women want the relationship to have meaning, men just want the sex. The less likely it is for the sex to mean anything, the better for him.
I'm not saying this is the case, just that is something to consider.
That is one of the hardest things about this whole situation. Let's say I 'give all' again...which is a very difficult thing for anyone to do. What's to keep him from taking the sex that is offered next time.
I cannot fathom that about men. If it's just sex, why marry at all? Why commit yourself to someone and promise to be faithful when all you really want is to get laid? Argh! (Not you, btw, just in general. ; *))