His interaction with that other female co-worker may have been exactly what you originally thought it was. When you say it was "inappropriate" touching, I take it you mean that it struck you as sexualized. My guess is that you're probably right. Do you monitor the interactions of all your co-workers? Or only his? If you and he were not in a friendship, would you have texted him about the interaction?

Why were you holding him accountable for this interaction? Are you concerned that he is betraying his wife? In other words, if he had not been married, would this incident have made you feel concern?

He doesn't like you critiquing his behavior. That may be because he is embarrassed that you saw him. That may be because he considers it none of your business. Is it?

I had an experience at work of turning into a hallway and seeing something that I was not meant to see. Two employees, a male and a female, were engaging in an embrace and an intimate kiss. The female happened to be married to another guy who worked there who was not the guy that was kissing her. The two kissers were obviously embarrassed when I stumbled upon them. She immediately launched into a lame story about how they had been kidding around. I made no query, acted indifferent and went on with getting to where I was going. I thought it was unfortunate that these two were not more discrete, and I hoped I wouldn't bump into something like that again. As it so happened, I didn't. I never mentioned the situation again to either of them. They both were good employees who got their jobs done.

I eventually heard through the grapevine that it was generally known throughout the workplace that these two employees were having an adulterous affair. I think my response when I bumped into the two of them was about right. I judged it to be, basically, none of my business. I did not see this kind of interaction between the two of them again. If I had, I may very well have taken the female aside. (I had some supervisory authority over the female.) Like I said, I thought it was unfortunate that these two had this relationship. (The female also had an adult daughter working there.) But, since there was no ongoing issue with their work performance and behavior, I saw no reason to not just let the incident pass.

When one witnesses behavior that really doesn't belong in the workplace, one can feel disconcerted, or even offended. That doesn't mean that rebuking the parties involved is always called for. In your case, swimfan, you texted him about what you saw, but you didn't text her. Why not?

This guy now sees his friendship with you as a liability. He feels threatened. It seems that you regret him thinking you challenged his "integrity." I don't think that is the main thing bothering him. My guess is that he is going to permanently distance himself from you.

You wonder should you offer him "a resolution." What is it that you think needs to be resolved?