So far you've only heard from men, so just wanted to say that from a woman's perspective reading this story, I also feel this was not a rendevous, but something imposed on him. Even if there was some level of "complicity" the comet thing seems to speak to a high level of shame, and not to a pleasent experience. In other words, even if he could have refused by some physical strength standards, and even if he experienced a moment of "getting into the experience", and even if he has some level of responsibility for allowing things to go so far, his reaction afterwards seems to clearly suggest that either he was fully forced or he was sent to a pretty bad internal space from which he acted out of his normal character -- so much so that he tried to wash it away with comet.
While I think some people might get carried away, then feel guilty and confess, while telling white lies about the lack of culpibility on their part -- "it wasn't me, it was them" -- not many would embelish with a story of comet, and especially, it seems to me, would a man think of telling such a story if it wasn't true. Male sexual pride runs too deep, making up a comet story just doesn't jive as a mere story.
He doesn't sound a filanderer.
I'm so sorry you're both going through this.