I just wrote this and sent it to her so here you go:
If you are still unclear on what you did that was wrong, here's a quick summary:
You received messages from him that you KNEW his wife and I would not like to have seen. Lines were crossed.
Instead of telling him you were married and not interested, you carried on trying to meet up with him even when he was at his most blatant and flirtacious.
You concealed the whole relationship from me - I don't know what went on between you two at <redacted>, the messages have been deleted. However at the time I read enough to make me very concerned. You should not have secret male friends that I don't know about, especially ones that are blatantly flirting with you.
You lied about the nature of your relationship with <redacted> in a counselling session when I mentioned him and afterwards when you said you were "just friends". Friends don't invite each other to meet up for a cuddle and a kiss.
Without going into detail I can't really give you more.