Obvious object of desire: when to walk away.

I'm a 34-year-old woman and my boyfriend is 35. We've been together for two years, and I’m currently pregnant. Unfortunately, my sex drive has completely diminished, and intimacy has become painful for me. Despite knowing how I feel, my boyfriend insists on having sex. I used to give in and just lie there, but it left me feeling degraded and less attracted to him, as if I were merely a sexual object. Recently, I've been firm about saying no. We've had open discussions about it, and he admits that he feels frustrated and deprived. I told him that I've never felt obligated to have sex in a relationship before. He seemed surprised that my previous partners didn’t cheat on me. Now I'm left wondering if I should end this relationship. I’m expecting a child with him and I also have another child from a previous relationship with whom he shares a close bond. Should I stay for the sake of the kids and hope he changes his mindset? I’ve raised concerns about what would happen if one of us faced an illness that prevented sex, but he just brushes it off. His perspective seems immature to me, and I don’t want to be with someone who views me solely as a sexual partner, nor do I want a relationship that centers around sex.