No matter how sympathetic you are toward the older daughter of the man you're dating, you should not feel obligated to put up with her rudeness. Her intolerant behavior not only could make you feel uncomfortable and belittled, but it also could drive a wedge between you and your boyfriend. You should attend to the problem sooner rather than later, as letting this pattern continue unchecked will ensure that you never feel welcome in the family structure, according to psychologist Marie Hartwell-Walker in the "Ask the Therapist" feature "Boyfriend's Kids Disrespect Me" for "Psych Central."
The Father-Daughter Relationship
Adult children of divorce report that their relationships with their fathers typically remain satisfactory unless certain curveballs are introduced, including the father's early remarriage, according to the 2003 study “Adult Children and Their Fathers: Relationship Changes 20 Years After Parental Divorce,” led by Constance R. Ahrons, senior research associate with the Council on Contemporary Families, and published in “Family Relations.” Whether or not your relationship seems to be headed quickly toward marriage, his daughter's dealings with you will not improve until they improve with her father. Encourage him to talk openly with her, reassuring her of his love, letting her know of his plans for the future and allowing her to express her concerns.
If he has not done so already, your boyfriend needs to step in and let his daughter know her rude behavior is not acceptable. If he has already spoken to her and nothing has changed, this could be because he does not back up his words with consequences. Influencing the behavior of a daughter who is grown and out of the house may seem difficult, but he can do so by promptly cutting off her tirades toward you or gently yet firmly letting her know she is welcome to participate in family dinners on Sundays as long as she treats you with civility.
Her Mother's Involvement
The mother can play a critical role in her daughter's treatment of you because of both the mother's direct input and the loyalty her daughter feels to her. If you and the daughter's father are serious, many of the dynamics of the stepdaughter-stepmother relationship may be called into play. And according to social researcher Wednesday Martin in the “Psychology Today” article “The Real Reason Children (and Adults) Hate their Stepmothers,” children of divorce often feel that by accepting their stepmothers they are being disloyal to their mothers. If your boyfriend's ex has bitter feelings, these will likely rub off on their daughter, who will, in turn, transfer them to you. Ideally, you could work out a peaceful relationship with your boyfriend's ex. If this proves impossible, you can help ease the tension by refusing to speak ill of the girl's mother and making it clear that you have no intention of replacing her.
Carving a Place for Yourself
Only you can determine if continuing this relationship is worth dealing with the rude behavior from his daughter. If you see a serious future with this man, you should attempt to establish a role for yourself, relevant to the daughter, that does not compete with the role of her mother. According to licensed social worker Jeannette Lofas of the Stepfamily Foundation Inc. in her post “The Dynamics of Step” on the group's website, it can be easy, when contending with so many potentially negative factors, to forget the positives -- namely that children, including adults, can benefit from the varied wisdom and experience of their expanded parental team. When you have a natural opening to do so, offer to teach your boyfriend's daughter a skill of yours, such as crocheting or cooking a particular foreign dish.