How do I not feel jealous tonight at bf's party (when he talks to girl friends)?

Ok, the boyfriend is having a party tonight. There is this one girl who's a totally platonic friend with him, but there was one time a few days ago I got upset and jealous about something she posted on his face book wall. I really was out of line, and took things too seriously. Anyway, she will be there tonight and I never met her before. Now, how do I not act all awkward and watchful between them? I REALLY have no reason to worry, I'm just so jealous sometimes. Yes, it's because I'm insecure. anyway, can you tell me what to tell myself to mentally and emotionally prepare myself? How to relax? I will be drinking, so don't suggest that.