I would like him to say, "I have been unhappy since January, and I am seeing someone else to see if I might be happier. It doesn't change how I feel about you, or my love for you."
If he insist on dating against her wishes, I think he should say, "I know you've stated that you're not ready to see me dating right now, but this is an important part of my personal growth, and I'll make sure that it doesn't affect you."
Ahoy, IMO, you gotta let this go. If he was capable of speaking about the situation correctly he would be capable of handling his marriage vows correctly. Rppfl is right. All you can do is lovingly be there for your daughter to pick up the pieces and remember that he's choosing to damage their relationship, not you.
I'm reminded of a scene from the movie Hope Floats with Sandra Bullock. The daughter is wanting to leave with her daddy and hes being a selfish a$$ and just breaks her heart and all mom can do is sit and wait to comfort her little girl.
Me 47 - W 35 M 9 - T 10 2 Daughters - 7 & 9 Discovery of EA- 8/4/14 S - 8/5/15 D mentioned - 9/11/14 R & Piecing - 3/17/15 Regard one another as more important than yourselves. - Philippians 2:3