I concur with Puppy--and I've been there. My 13-year-old D completely figured out that her father left us because he was having an affair, even figured out who it was with. And when she asked, I was honest with her. Her father continues to place 100% of the blame on me and denies to everyone, including D13, that he was/is having an affair. And she resents the heck out of that, doesn't trust him for anything, has a lot of anger but is generally afraid to express it to him because he threatens to "ground" her. And she is afraid that, since he stopped loving me, he could stop loving her--and to her it feels as if he has, because he's so "into" his new family.
But because I was honest, and because she feels she can talk with me about anything and express any emotion, we've had some very positive conversations and remain very close. She doesn't hate her father for this, but she recognizes how much it has negatively affected our lives.
M60 H52 D20 M14 yrs OW-old gf from 1986 bomb-5/18/08 H filed for D-9/10/08 D final 4/24/09 xH remarried (not OW) 2012