I'm so sorry you're hurting, what an awful situation to be in. Here, have a cyber hug ((((Trying2live))))
First of all, this thing going on between your husband and his ex coworker is NOT a friendship. It is an emotional affair.
Please read 'Not Just Friends' by Shirley Glass, it will help to clarify things for you. Your husband should also read it. Hopefully it will be the 2x4 he needs.
Second of all, no BS can say that the wayward's affair was 100% the wayward's shit to own but then justify their own affair with the pain caused by their spouse's betrayal. Does that make sense?
So a BS cannot say "Your A was because you were broken, mine was because you cheated first." Shit owning is a two way street.
Personally, I don't think revenge affairs exist. It's just another affair because the BS is broken in their own way. Yes they've been handed a lot of pain but not all BS' go out and cheat, most have adequate coping mechanisms.
My rather laboured point is, yes you are justified in feeling hurt by this. It is not your fault.
Is MC an option at the moment? Is your now WH in IC at all. You can have deal breakers too, you know.
Sending strength. Me - 27
Him - 27
My Ddays - Jan 2010 & 12/04/14
His Dday - 23/12/13
Chin up. Unwavering. Fight. I can do this.