Knickyknock, I think you have handled this beautifully on the basis of the information you had.
Now new information has come out and it's very clear your Husband was on the path to having an affair, but the reality -seems- to be that he didn't yet. In fact the month of sexual emails last year came to a close (who brought it to a close, him or her?) and it sounds like in fact your husband was putting this woman this year off rather, rather than being keen to meet her and complete the betrayal.
Without doubt he needed a very sharp wake up call. It probably came came just in time.
But he didn't actually consummate the betrayal. Not yet. Because you found out in time, he may not ever - he's obviously very shaken.
Not saying what he did is right here, highly sexual emails with others and (at the least) a kiss is not right at all. But equally it could have been a whole lot worse.
It's possible that if he and you both have time to think, something can be salvaged from all this. Men, well, people, do sometimes get brought up sharp and have to think about what they really want and decide that their wife is way more important than cheap affairs.
I'm suggesting you at least talk when you are both calmer and keep in mind that in fact, your husband and the OW didn't do the dirty. From the info you had, you did everything right. Now you have new info, and in reality he does seem to have avoided meeting the OW and the finally breaking your trust and his own decency.
I hope that whatever you decide, you can stay as strong as you have so far and are able to take care of yourself hugs