Uncomfortable Around My Extended Family Options

[Little Bird]

Hey,

This weekend my Mom, Dad, little sister and I are going to my aunt's wedding. I am fine when I am around my mom and sister, and even my dad. However, when I am around my extended family I can't seem to say anything that isn't angry or I just don't say anything at all. I don't have any problem making friends at school or talking to other people. My cousin, Al, and I used to be very good friends until around four years ago when he stopped talking to me. In return, I stopped talking to him. When that happened I began getting increasingly uncomfortable with other members of my extended family. I was hurt that for some reason or another, Al seemed to hate me. Even though he doesn't like very much he is friends with our other cousin. That particular cousin won't be able to make it to the wedding and so Al's mom told our Grandma that since he would have no one to hang out with then he was allowed to bring his girlfriend to the wedding. I don't think this is fair to any of the rest of us. I go to visit my extended family frequently enough and I never have anyone my age to hang out with so I don't understand why he souldn't just suck it up for one weekend which is exactly what I am going to do. This weekend is my aunt's weekend and I don't want to spoil it even the tiniest bit by being a bitch. However, now I angry at my aunt and cousin and very uncomfortable and nausious about having to meet his girlfriend. I haven't told any family members other than my mom and sister about my anger because, again, this weekend is not about me. It shouldn't be about Al either and I'm afraid that I'll say something horrible. This weekend I am going to be a well-behaved and kind lady so that everyone else has a good time. How do I do this without losing my temper and what are some ways to overcome this feeling of discomfort around my extended family.