Reasonable?

Here's the story so far in as brief terms as I can make it.
About a month ago my boyfriend and I went to his best friend's party, and there was a girl there who was all over him. Admittedly she ended up passing out but she was flirting like crazy. I had to leave early, and everyone who had been at the party were chucked out so they all went to this other guy's house. My boyfriend said that in the morning he woke up in the same bed as this other guy and the girl who was flirting with him. Although he said nothing happened, and my first instincts were to trust this, I couldn't help but hate her. Even seeing her online without talking to her I just get so worked up.
Anywho, today, he, his best mate and this girl went into town all together. I'd asked if he wanted to meet up and he said he couldn't make it because of this. But it didn't seem like it had been planned before today. I've been fuming all day and I can't stop feeling angry. I'm not usually a violent person but it took one hell of a lot of self control to keep myself from trashing my house.
I guess what I'm asking is how reasonable is my jealousy? And how can I stop myself feeling jealous over her? He's said to me on several occasions that I haven't got any reason to be jealous but I can't help it.

Jam it back in, in the dark.

well if I guy wakes up randomly with a strange girl in his bed...that usually means one thing (even if the guy denys it >_>). They were drunk afterall

There's nowhere I can't reach.

wow that blows, maybe you should actually talk to him about how you are all pissed off. You know guys have no fucking clue what is going on in your head.

This thing is sticky, and I don't like it. I don't appreciate it.