In my practice, I have seen on several occasions instances in which an older sister will try to undermine her younger brother’s romantic relationships . Sometimes this can show itself by rudeness whenever the girlfriend or wife is around. Or it can begin when there are family events planned and the wife or girlfriend is not included.
This often happens in families in which the sister at some time in the brother’s childhood was made to take a maternal role due to the mother’s death or illness or even neglect. In this family dynamic the younger brother is never seen as grown up whether he is 19 or 49, the sister assumes she knows best. She has taken on the role as her brother’s protector even when he has long outgrown the need of a protector.
Often the brother feels torn between his girlfriend and his sister and family members. Even though he know that he should stand up for her and let his family know that his romantic choices are his alone to make, this may not be behavior that he is used to. However it is important for the family to be told that they must be cordial and polite and inclusive of the brother’s wife or girlfriend. Once they know that he is going to stand up to them, most often they will back down and start the acceptance process. In the mean time, its important the the wife/girlfriend understand that the behavior was not meant to be malicious but simply was a way to protect the “little brother” of the family.