I would tell your son that you are sorry that his dad is not there as much as your son would like him to be and that is not anything that anyone can change. That your son is welcome to say something to his dad, and that you know, in spite of how dad is acting, that dad loves him as best he can.
BF sounds like a douche. But as the CP, and the only responsible parent, you need to try, IMO, to preserve your kid's self-esteem. He thinks something is wrong with him and that is why BF is a douche. Gently let him know that is not true, that you and Dad love him to pieces but that you show your love differently, everyone does, and you are sorry DS is hurt.
I think it's up to the kid to boot the parent from their life. If you are the good parent, don't badmouth the bad one. Let your kid think OP loves him very much, and let the kid at some point boot dad from his life for being a douche. Good luck.
at 3:40 PM on Jan. 11, 2010