Boys night out

Hey girls! I need some advice on a situation that shouldn't even be bothering me. So.. my bf of almost 6 months, whom I love dearly, decided to go out with the boys. From the time we started dating, he has never done this. Everything has been great between us. He has never given me a reason to not trust him. Why am I feeling so bad and uneasy about him going out with the guys? It was a last minute thing with him and the boys and he has work early in the morning. I guess that's why I'm freaking out so much... any help?