how about looking into counselling as a couple? i think you need to hear why he is still with you.
fwiw, it was me who had an affair, before i get flamed (ive been with my dh 22 years, 2 kids), i had an brief affair after a trauma in my life 17 years ago,it was after something terrible that happened to one of my children, (one of my children became gravely ill, and my DH left me alone to deal with that, we seemed to grow apart afterwards) i had no idea what i was doing i just need an escape, i wanted out of my life.
but when the shit hit the fan my DH was incredible, we went to counselling as a couple, we talked and talked, we examined our feelings, we looked at external factors, we looked at the whys and the wherefores, we understood what had happened, we put it to bed, and moved on, and to his absolute credit he has never once brought it up again, and nor have i. i was so ashamed, but i think because we did counselling as a couple he heard me when i told him why i was with him, and why what had happened had happened. He was not totally blameless in the break down of our relationship and he took responsibility for his part in that.
i do believe that the counselling as a couple saved us. We both learned alot from it. i knew i couldnt live a day without seeing him, i had my own guilt to deal, the only way i think you can get past an affair is to do exactly that - get past it. I dont think you can get past it any other way than by exhausting all the questions, talking it through and then. finally, letting it go. I think if it keeps rearing its head then its very hard to move on, thats why i think counselling is invaluable.
i was very lucky in that we both managed to do that. I hope i dont get flamed for admitting this, i just wanted to be honest.
i wish you both lots of luck and i hope it works out for you op.