D.T.
C.,
I empathize with what you are going through. Now with that being said, can you see where your daughter is coming from? Your boyfriend is not her problem. It is your problem. Your 12 year old did not sign up to have her parents divorce and then before she is an adult she has to take a back seat to not only your boyfriend who may assume he can step in to tell her what to do, but now she has a baby brother. She is pre-adolescent which means she has a lot of hormones raging through her. This is a time when she is exploring who she is. Her values in life are being clarified and shaped by your example, her moral development as well as bodily changes are changing and developing. She is making choices that will affect her for the rest of her life. You state that your boyfriend doesn't want to be around her because of her attitude. She probably doesn't want to be around him because of his attitude (what is he 12)? And your relationship with him is rocky. Can you not see she is acting out how you feel about the relationship? You are the adult, not her.
You and your boyfriend need to go somewhere private to talk about your relationship (do not make the 12 year old babysit). Afterwards, be the mom you promised to be to all of your children when you choose to have them.
About me: Therapist, married 26 years, 2 grown children