Your H feels entitled to break the boundary that he previously agreed to so that he could have a secret 1:1 drinks date with OW. Now he is gaslighting you by downplaying both her romantic gesture and his keeping the secret instead of feeling mortified and apologizing to you.
@Saladdays01, are you thinking that (1) they’ve already been crossing lines and he stopped the kiss because they were seen or (2) he pulled away because she breached platonic boundaries?
Did he know that your Friend was around? If so, of course he broke away awkwardly and made a joke.
And yes, OW has been using you and feigning friendship to keep you close and throw you off the scent while she lusts after H. The question is, have they actually been having an EA or PA? I believe so.
In my view, your initial niggles were valid. H weakened his boundaries and opened a window to OW months ago, and has been flattered and validated by her intense interest. They’ve been getting closer via proximity, attraction, over-familiarity, and confiding. It sounds like they have an intimate KISA/Damsel dynamic and are firmly in EA territory which possibly led to some physical involvement prior to the public kiss. It didn’t come out of nowhere.
@Saladdays01, it is very troubling that H intends to prioritize OW by continuing this inappropriate relationship. Even if by chance it is one-sided (it isn’t), he cannot justify disrespecting you and your marriage by continuing contact with this woman who kissed him. You’d be very foolish to tolerate that degradation and the anxiety it will trigger.
If this were my H, he’d be dropping OW, coming clean, and taking full responsibility for his faithless behavior or it would be game over.