I understand how you feel as about OW's presence in you D's life. It's a horrible feeling to feel like we are helpless in taking any action when something is so painful to us. I think though that you are doing a wonderful job in trying to put your D13's comfort first in not making a "big deal" of it. That would just give D13 pain, because she loves you and doesn't want to see you in pain......not to mention the power and validation that it would give to your XH. I know that your D13 sees your strength and dignity in spite of pain (which I have no doubt she knows you feel) and will thank you for it someday. And she will be the better woman for having you as an example.
As for the potential relationship, I recently read a book titled "Getting Past Your Breakup" by Susan J Elliott that really helped me. In it, one of the things she talked about was how our relationships are a reflection of where we are, and how to avoid "rebound" mistakes and how to work on ourselves so we can build healthy new reltionships, and how to recognize when we get one. Anyway, check it out.
Take care!
TJ
Me45,H49 D24,S18 M26,T28 Bomb 3/19/08 Sep 6/23/08 EA/PA with Secretary 2007-8 3/2009 H moved in w/OW2 7/2009 Let him go w/Love. 8/2009 Legally Sep'd