text: is it normal for a younger sister to be overly protective of her older brother and who he dates? a younger sister who was once very friendly towards me got very stand-offish with me once she realized i was dating her brother. is this normal? and why would she act this way if she did like me to start with? i think it is fairly normal. i am a younger sister to three brothers and i think it can just make you nervous because you don't want your brother to get hurt and their is girls stepping into your territory. at first i  did'nt like any of my brothers girlfriends but after a while i was ok. just give her time she'll eventually come around.