Have you ever spent any time with your colleague outside of work before? With me personally, I haven't spent any time with anyone from work outside of the workplace. Except a couple of times and I didn't enjoy being at their homes. They seemed to act different at home than at work; seemingly nicer at work than at home. If you have a personal policy that you don't spend time with anyone from work outside of the place, you can say that about the dinner invitation.

I'm sorry to hear about conflict with your colleague after having a pretty good amount of time of a good relationship. I can't count how many times that's happened to me. A real nice relationship with a co-worker and then a blow-up. There were times when we'd make up somehow strangely. Me and the other person never apologized to each other.

I may be wrong but it sounds like he might be trying to make up with you. I think it would be better for him to try to make up with you instead of going through his wife. If there's a chance to make up I would try to take up on it. That's just me. I know it's hard to try to make up after a conflict. Maybe something will happen to bring you two together. You said you didn't want to "trash" the relationship. Best to you!