Hello my friend. When you have a relationship with another individual, you are entering into relationships with other family members as well. Dealing with a teenager can be very difficult, especially as the girlfriend of her father. It sounds as though you deeply care for your boyfriend. His daughter has come between you and your boyfriend. You are in an awkward position because you are not married to your boyfriend. The daughter probably has spiteful feelings toward you because you are in the position that she probably wishes that her mom was in so that the family could be complete. But that is not the case obviously. You have even stated that you are not going to jump into the family dynamics like a missing puzzle piece which is good. However, for things to get better, then everyone must be open and honest about how they feel. You, your boyfriend, and his daughter must all sit down and have a discussion. Your boyfriend should start the discussion by saying that there is tension in the household and that things need to be resolved. Then your boyfriend can ask your daughter how she feels about you. Let her speak until finished. Then you can explain your feelings but try to not to be too harsh but more respectful. You do not want your boyfriend to feel like you are threatening his daughter. Putting all the feelings out in the open is the best course of action. If everything is kept swept under the rug, nothing will change. Also, do not confront the daughter alone. That would probably make your boyfriend extremely irate.