is it weird that i get mad when my best friend brings his girlfriend along?

[Coralee]

I've been very, very close with this guy (I'm a girl) for a few years now. At the beginning of college, we used to hang out all the time--just the two of us--going to movies and dinner and even just hanging out and talking at his house. It was that way for a few years. He's been dating this girl for about a year now, and I can't stand it when he shows up at my house with her. I know they're dating, and I respect that, but he and I had a really special relationship and we talked about really deep things together, and when she's there, it really changes the dynamic. Is it weird that I want so badly to be alone with him? He won't even warn me that she's with him. He'll be like "hey let's meet for dinner," and when I get there, she's there too. I hate it so much, and I end up pouting all through dinner because of it (which I know is immature on my part). Do I have a right to spend time alone with him even though he is in a relationship? And if so, how do I approach this without sounding possessive?