At a loss for words!

I am so upset...and somewhat at a loss. My ex-husband has been planning a trip with his girlfriend to see her oldest daughter graduate from basic. When they first told dh and I about it we told them if it happened to be our week w/dd we would let her go with them if they wanted. The time has come they leave wed. and not only did my ex-not talk to my dd about it he didn't even tell her she wasn't going! Apparently dd heard his girlfriends son ask "is she going" pointing at dd....the answer she heard was no. Then they were at Wal-mart where everyone was picking out cup holders for the trip and when dd asked where they were going his girlfriends son told her she wasn't going....and that was it. No one explained to her why she wasn't going....no one told her why they were going....aaarrrrggghhhhh...I'm so angry. I held her last nite while she cried because she doesn't understand why she can't go. I being the big 'ol mean ass bitch that I am called the ex to tell him what an ass I thought he was and that he had broken our dd's heart. Like always he didn't seem to care other than about the fact that I was yet again making a big deal out of nothing. As If!! I'm her mother if it was some stupid little boy that had broken her heart I would know what to say....Like I would think most mothers of daughters I started planning out that speech when they said "it's a girl", but from her daddy....most all little girls put their daddy's on such a high pedestal anyway....So after my protective mother speech to my ex I came out of the bedroom....'cuse I didn't want her to hear that conversation....and my dh told me that she had made some interesting comments to him while I was out of the room. Apparently she told him....she didn't think it was fair that she wasn't going...it was supposed to be a family trip and she's part of the family....ok that just broke my heart....I know my dd's not stupid....believe me keeping up with her intelligent mind is half of my life's work....but for some reason I guess I was just leaning on the idea that she didn't think about it that much....that she didn't take it to that level....I don't know why but it bothered me all the more when I realized she did. I have noticed for awhile the difference in her dad's behavior not just where she is concerned but in him in general, I didn't think she had noticed anything though....I had a long serious conversation with her today after school and I have misjudged the situation totally....now please don't misunderstand I am a very attentive mother, I ask her all the time whats going on....how are things....is everything ok with you....I guess she just didn't feel the need to break it all down to me until today....but from what she told me today she has not only noticed a difference in her dad as well she feels he treats her differently....and not in the best of ways....as a mother I'm at a loss....I can only tell her so much and so much more she is gonna have to experience and decide on her own....I had hoped my dd would not have such grown up issues to deal with. I guess what they say is true....divorce is hell on the kids.