SIL with brother.

My sister in law has one of the nicest asses I have ever witnessed, and as for as long as I’ve known her I’ve wanted to fuck her. Recently my brother hit me up one night late so it was very unusual, to come over. I went over and and they started talking about going to bed as soon as I got there so I was pissed because I felt they played a joke on me. My SIL looks and says you can come to bed too in about 2 minutes. I was confused at first then when she called me in the room she was naked already playing with her pussy I immediately looked away and then my brother walked up and said you ever been in a threesome? After some thought I went through with it and tag teamed my SIL with my brother. Apparently it was something she always wanted to happen but not with a random guy so she chose me.