XH told OW (who happened to be a friend of mine!) that I was:
unsupportive, was uncaring, didn't understand him (etc etc. You know, the usual Script). Oh and that we'd split up.
Truth was: I was the breadwinner; I was supporting him and doing my best for him; I was trying to coordinate (and pay for!) multi-agency help for him to get sober/clean (whilst working FT, keeping the house in good nick and parenting the kids); that we'd separated (temporarily) in order for HIM to get time/space to get sober/clean; that we were working on saving the marriage (that had been wrecked through years of his addictions, and abuse from those addictions).
As a supposed friend, she could have spoken to me, or asked me how I was doing or what was happening. She never did. She either fell for the lies, or conveniently chose to ignore the truth (or try to find out the truth). I believe in her case, it was the latter.
Now, he made the wedding vows to me, in front of our families and friends. He broke them, which is disgusting. He could have just dumped me first/ended the marriage and then gone off with her (I would have had more respect/acceptance of that), but he chose to behave in a disgusting and deceitful way. She didn't make any vows (but she was at my wedding so knew fine well we were married, and she knew we had young children), but I still, to this day, can't understand how a friend could treat another in such a way.
In hindsight, they both did me a big favour. I will never trust anyone again like I used to. And my life is a lot more peaceful now than it was. Still, a few months down the line, she (and he) came crawling back after they split up.