Well, what is the basis of your issue with what he did? You say you can't stomach looking at him, but it's been a couple of months so you've had time to process what you think and feel about it, you must have more than a gut reaction.

People have been referring to it as "cheating" - my question is, what about this incident is bad: the biological exposure to another sexual partner, the idea that he has emotionally connected with a different person, or the embarrassment that he may have exposed his (and by extension, your) sex life to others?

If it's the biological exposure, that would be reasonable if he hadn't told you about it before the next time you had sex. If it was the emotional connection, that would be reasonable if it was with someone he knew. If he had connected with someone who offered him something he found lacking in your marriage, that's something you should talk about together and work through, as it's common and often fixable. However this is unlikely given the circumstances of what it was.

You haven't said that it was in front of his co-workers or that they knew anything about it at the time, so I'm still trying to pin down the exact reason you are shocked by it. Is it simply because it was a sexual act, is that enough to throw away a nearly decade-long commitment? (The facetious response here is "it was for him", which is unhelpful since we have no evidence that he was thinking in those terms).

The fact that you haven't been able to confront him with an explicit breakdown of what you find disgusting and why you feel your trust has been irrevocably broken makes me think that this marriage was lacking in communication already.