I can't believe someone suggested she apologise to this guy.
The way I see it, this guy is a massive sleaze and has successfully manipulated the situation so that the OP is feeling guilty about it. Every new situation in the evening was led by him.
OP, lesson learned about the booze because it clouded judgement and led you down some shady territory. Don't worry about it, you are the single girl in this situation and he is the attached one so no blame there. He probably had his beady eye on you from the beginning of the evening, you are a good mark. Absolutely don't feel guilty.
A similar thing happened to me, a married colleague who is not unattractive, with 3 young kids, not a boss, still awful. I was single. Started off on a night out with loads of friends, whittled down one by one to me, him and a couple of others. Went back to one of their houses (not mine or his) and he tried to kiss me, and when I resisted he mumbled something about how loneleeeee he was and that crap and I spent the next 2 hours listening to his woes instead of slapping his fucking face, I gave him a hug at the end of the evening. Urrrgh. Next day in work he didn't show so I texted him took on all the guilt and made it all better for him. He said his modus operandi was not to go about doing this sort of stuff and I forgave him and apologised for my part in it (what that was I don't know because I never pursued the guy) but came away from it sort of fancying him and never had that feeling before, it was weird. Work was so awful and so awkward.
I now know I went through some sort of trauma bonding with this person. I had been single a long time and that hug was the only one I had had in two years, and even though I had technically been sexually assaulted (I hadn't wanted to be kissed or thought it was going to happen), I made it my fault, not his. Turns out a few months down the line he acted inappropriately with another single female colleague, and that's how I started seeing him for how he really is. I have anxiety issues too, and past history of emotional and sexual abuse and that mo'fo set me back.
The best thing to do about this situ, own your part in it (alcohol) and no more. This was his creation. And you can always do the obvious thing, pretend total amnesia after the second pub. You have done nothing wrong. Style it out love, I could tell you a few stories, and a lot of people are saying the same, don't worry,