If he bawled he obviously cares more than you thought.

Work out what EXACTLY you liked about Sunday guy.. was it the sex? was it the way he made you feel? (it sounds like the second one).

Now are you serious about your marriage?
Talk to XH and tell him how being with someone else made you feel, and why. Tell him that its something YOU and HIM have to work towards achieving together if he wants things to be a success.
You need him to make you feel like Sunday night guy did.

Tell him that.
If he is so upset about not being with you, surely he will try anything.
Good luck hun xo