I am so very glad you wrote. The situation you describe is serious for you, your coming baby, the little girl, and her father. Yes, some of the intensity of your feelings is because you are pregnant. But that’s not the whole story. You’ve been in this little girl’s life since she was born yet your relationship is so bad. You don’t mention what your partner is doing to help. You don’t mention whether there is a healthy collaboration between you and the girl’s mother. And, most important, this little girl isn’t acting like a normal 3 year old. Three year olds generally don’t act in sexualized ways such as you describe unless they have been repeatedly exposed to inappropriate sexual material or they have been sexually abused.
You’ve been so upset by your stepdaughter’s behavior that you haven’t been able to see the scared little child who is underneath the provocations. Stop fighting and competing with her and get her some help. She needs your compassion and support, not your hatred. I certainly hope her dad’s attention is entirely appropriate. It’s important to think about who has access to her and who might be hurting her. She needs to be taken to a child psychologist for an evaluation and she needs loving adults around her to help her.
If your partner isn’t concerned about the situation you describe, he should be. You two are long overdue for a serious talk. I don’t know if he really isn’t giving you enough attention or if you are so insecure that you need more attention than you should. I don’t know if his attentions to his daughter are inappropriate or if he is compensating for your behavior toward her. You and your partner need to talk about how you are going to give adequate attention to two children and not lose sight of each other’s needs as well. If you can’t do this on your own, it would probably be helpful for you to see a couples counselor. Please take the next few weeks before the baby arrives to get some sessions and to create a better environment for your growing family.
You may be only 17 but you need to act more like an adult and do some of the things that need to be done. You’re going to be mothering two children who need you to be your most mature self. All of you deserve a more peaceful and emotionally healthy household than you’ve got.
I wish you well.