I am 18 years old. I hate being jealous, it's the worst feeling. But she's my friend too. And I don't see him that often, and they go to the same church, AND she is best friends with his older sister (he is only a year younger than me). He talks about her sometimes, and I can't help but feel that he would rather be with her, even though she is taken. She is a bit of a flirt and so is he. And I am on the quieter side. But he calls her his best friend, and its getting me worried. Do I have a good reason to be, or is it all in my head?

Oh, I guess I should add that they text every day, and chat on fb and stuff. Nothing flirtatious, I don't THINK... but I can't be too sure.

Is he your boyfriend or just a friend?

He is my boyfriend. We've only been going out for a few months, and he has known this girl for a few years, and liked her in the past. But he told me he loved me, and this is his first relationship.

You have only been dating a few months. I take it he has been talking and texting this girl for a long time, before he started dating you.
He chose to date you. Get over it or break it off. They seem to be friends.