I don't think anybody on this thread is suggesting that her actions were any less morally dubious that your H's but she had not made any promises to you, he had.
That is the difference.
If she had a partner, they would be in your shoes and have every right to be very hurt and cross by her behaviour, not so much your H's.
I totally understand where your hurt feelings are coming from, but apart from the fact that you have no legal leg to stand on, you are sadly directing your ire at the wrong person.
I don't want my husband to be a liar and a cheat, I don't want to know what I now know about him, the man I've known for 25 years, have been married to for 20+ year, have 4 children with, but other than a time machine there is no way I could be back with him as a couple as I simply can never trust him again. He has proven by repeated actions, just as listed by Walkaboutwendy that he is capable of underhand and deceptive planning and repeated lying. If it had not been with this OW, it would have been A.N.Other.
I am gutted, and I can truly empathise to how you are feeling. I do still want my H back, but actually I want the version of him back that I thought he was, not who he actually is and there is no amount of blaming the OW that will make him what I want him to be.
I know every situation is different, but you are hurting for very obvious and understandable reasons and I am very unsure that blaming the OW (letter or no letter) will allow you to move forward.
