Sorry so long, but I am DESPERATE

To begin, I am a 31 year old mother of an amazing nine year old. I am also in an eight year relationship with a man that is my heart and soul. We are expecting a baby in May. He is older than me by many years, but to be clear, he is not rich and that is not why I am with him. My son't biological donor taught me so much about what i wanted in a man. He has never even asked if I had a boy or girl and has no monetary or other responsibilities when it comes to my child. That is fine with me. He had a drug problem and I would rather protect my son from the hurt and disappointment and selfishly, I don't have to share my time with my little man. He did teach me that age and maturity made it hard for me as a twenty something year old single mom to meet someone who shared my life goals around my age. Enter my OH who has raised my son like his own since my son was a little over a year old.

Now the other side of the store. My OH is older and has older children. We did not start hanging out or dating until after he was divorced. (please keep in mind it has been 8 years now). His son and I get along relatively well. He has always been respectful to me and to my son/. He is naturally quiet and is very relaxed and go with the flow. If anything, he and his father's relationship is stronger than before the divorce. They make time to spend together and see each other almost every day a week. His daughter is a different story. In the beginning she was 14 years old and would not come into the house if I was there and has never even spoken a hello to me. She and her father have almost NO relationship because she will not address him. Even at his father's funeral last year, she would not look him in the face or acknowledge his existence. That is until right around Christmas time and right around his birthday when she has annually sent him texts saying she wants to fix things and then backs out saying that with me being in the picture at all she can't do it. he has ruined her life etc. She has vandalized my car, sent me nasty texts, called me a bitch in front of my son when she did come over to get her Christmas gift... They have tried counselling.. He says that at this point, he doesn't see her ever getting over this and building a relationship with him.

My heart is broken for him. Family is the most important thing to me and i have begged him to continue to reach out even if he is hurt and to see if they can build a relationship separate of me and my son because I cannot imagine.. My OH told her that we were expecting a baby and she replied with venom and I asked him to take a few days to let her soak the news in. She won't respond to him and now that I am six months pregnant, she has text her dad to say that she wants a relationship with her sister, but cannot stomach to have to deal with me or my son. I can tell you my thoughts on this, but I don't want to regret my response so PLEASE HELP ME and let me know your thoughts. I feel like i ma going crazy. The only thing i have ever asked for is respect for my son and I...