You feel partly to blame - how?!
What else can you do... Well, for a start, remember that you are a catch. A dignified, ADULT person who doesn't embarrass themsevles by drunkenly groping colleagues at a party. Who deals with a situation when she sees it instead of hiding in a sulk with a duvet. Who thinks of her children first. Who is, honestly, far too good for her lying manipulative shit of an H.
A woman like you does not need to cling. If I were you, and had decided to go to this dinner tonight, I would take the following approach. I would be the Ice Queen. I would be cool, dignified, aloof. It would not be possible to please or entertain me, my thoughts would be, very obviously, elsewhere, although I would be polite and amenable. I would make it clear, if asked, that I had no idea how things were going to pan out. That I was considering my options, because I was crystal clear that what happened last night was that my husband cheated on me, and that I was not willing to continue in a marriage of that kind.
And at some appropriate point in the evening, I would say 'I just want to make one thing absolutely clear to you. I will not live with this kind of behaviour, and I am not frightened to make the decision to leave you and go it alone if you want to act this way. Because, if you do continue to act this way, what I will decide is that you are not a man worth having, and a life with you will be irritating, dishonest, petty, depressing. So think about what YOU want. If you want to show me that you are that kind of man, you'll essentially be making the decision to see your children grow up without you, most probably with a stepfather that I'll have decided is twice the man you are. How you want your life and family to be is up to you, but believe me, if you decide that a cheap grope of an equally cheap colleague's bum is worth more at that point than your family and home - then you forfeit any right to have me consider your feelings when I consider MY future.'