RTL, Try to stop beating yourself up. Your W should have assigned blame to you with your D. D probably asked her why she left and you could not be together, she should have just said you could not get along or something. W should never have said it was something you did. She is using emotional balckmail on bot you and your D. She is just using the fact that she knows you want your family back together to gain sole custody. Be aware and while there is always blame on both parts, protect yourself.
