Well, technically she didn't really lie to you because she did admit she had sex with that other guy. The way you wrote about that though it sounded like it was said sarcastically, but now you know because she has talked about it elsewhere. I think part of you knew and part of you was hoping it wasn't true. And she hasn't seemed to express any guilt about it according to what you have shared.

I am sorry (((Dad))) because I do know what that feels like and how much anger it creates too. Truth be told, I never really got over it, it took something from my relationship, the trust took a big hit and the "I love you's" did not hit where it should have after that.

Take care of yourself and keep a distance so you can slowly work through the emotions you are having. I hope you are still working with a therapist because it will benefit you from having the therapist help you work through this. It's important you be strong for your children and you make sure you let them know how much you love them.