If he wants to stay with you, C is a must. No excuses. He will continue to have feelings for the OW and if not her, then someone else until he figures out why he did it in the first place.
I understand about the fighting, but let's face it, it takes two to tango. Even though you two fought, you never went outside the M. It was a shortcoming in him. He needs to take the initiative to do something to heal the M.
Instead of GALing by going out with others, how about just taking on a hobby, or just take long walks, or anything else? You might even consider withholding sex for awhile. He has to miss something about you.
M-43 W-40 2D - 9 and 5
Emotion, yet peace. Ignorance, yet knowledge. Passion, yet serenity. Chaos, yet harmony. Death, yet a new life.