I'm such a jealous idiot

I saw Mark talking to Sarah at the party. I *know* they're just friends, but... ugh. I hate this feeling. It's like a knot in my stomach. He's so charming, and she's so pretty and smart. What if he realizes he could do better than me?

I spent the whole night trying to act cool, but inside I was just dying. I kept finding excuses to pull him away, or make little digs at Sarah. I'm sure I looked like a complete psycho. He probably noticed. I feel so ashamed now. I should trust him. He always tells me he loves me, and he shows me. But I can't help but feel insecure. It's my problem, I know.

I need to stop being so jealous. It's going to ruin everything if I don't. I think I need to talk to someone, maybe a therapist. Before I screw up the best thing that's ever happened to me. I just don't want to lose him.