I was pondering this question a while back and came to the following conclusion and would like TRP's take on things:

"Exclusivity means restricting intimacy to another person (the one you agree to be exclusive with). However, if the two of you are not being intimate, and it's because one partner failed to live up to their end of the agreement that forms the basis of the exclusivity, then they've broken their end of the deal. Therefore any intimacy gained by the other partner is free and clear of any accusations of cheating as the couple is no longer exclusive, and possibly not even romantically connected. Relationships without intimacy are simply complicated friendships."

Athol Kay talked about this a little bit in the Married Man Sex Life Primer, which helped shape my position on things. I know, I know, this is very counter-feminine imperative thinking. IMO there's not much worse for a man who values sex in a relationship than getting suckered in with a promise of intimacy and then the woman backing out of her end of the deal. It's a classic bait & switch. Another is a woman being thin to land a guy, then piling on the blubber after she's got him locked in. On the back end, is guys who see their girlfriends get fit for the wedding and then balloon back up after she doesn't have any bridesmaids she wants to outdo. To those guys, my advice is to articulate that if she can lose the weight for the wedding, she can keep it off for you since you're more important than anyone else there.

tl;dr - refusing sex breaks the agreement being exclusive is based upon same as if someone cheated