I'll try to explain, so pardon any mistakes or misjudgments i write here. For me, it had nothing to do with sex, or love for that matter, it was the risk and newness that got me going. I still love my wife, never stopped loving her, just in my mind i needed more than she could or would provide. I dont mean that as a knock against her, its just how my brain rationalized what i did. Now that i dont have that raging sex demon inside of me (thanks meds ) i can now concentrate on the love i have. We have precious little controll over ourselves when this stuff strikes. He probally loves you greatly, and in his mind only had the affair to "save" his marriage. Trust me, we can rationalize really well, and he can to. This probally made good sense to him at the time.
Its hard in words to put this out, it just "is" what it is.
Sorry i havnt been more helpfull. Bill