My bf's brothers girlfriend..

My bf and his brother are very close and love to hang out. So of course we go on double dates and all hang out together. I've been with my man for almost two years now and they've been together for about a year and a couple months. When we first all started to hang out we would go to the bar, or go to the movies, and have a really good time. One time we were all drinking at my bf and I's place and she was wearing a skirt and I felt like she was acting inappropriately not keeping her legs fully closed. Instantly I got upset I don't care how drunk you are, if you're a lady keep your legs closed! After that we didn't hang out with them for a while because I was upset. My bf and his brother didn't see what I was talking about I guess.. I decided to be the bigger person and just get over it for my bf. So they invite us over and we go and whenever we invite them over or to do something my bf's brother says he has to ask her and she literally always says no. I feel like I'm such a shitty situation..