But not right! Moral issues aside, you are doing this behind your W's back. In purely practical terms, do you have a plan for when she finds out?
I have no control over her reaction, and I'm sure she would experience a whole spectrum of conflicting emotions. But as for my part, I would end the affair. That had already been mutually agreed on before the affair went to the physical stage. I assume my wife would lose all trust in me, but I would respond by being as open and honest about everything as she is willing to take. Has she noticed I am more relaxed, more happy, a bit more alive lately? Is she willing to make the effort to deal with my sexual needs, in order to have a happier husband? The other choices are divorce, or simply don't-ask don't-tell. My honest feeling is that sex, if not important to the marriage, can be handled like fishing, stamp-collecting, or other hobbies that meet personal needs not addressed in the relationship.
But I'm also considering seeing a counselor on my own, because I recognize I'm not the best judge of things right now.
