How do I curb my jealousy and make amends to my girlfriend for it?

My girlfriend and I are the "geek couple" in our respective families and social circles and are both the subtle butt of jokes made by friends and colleagues.
I joined her for drinks with her and some of her male colleagues - she's the only female team leader on her floor and the others were team leaders I've met before. This was on Friday night and I expected the usual gentle humour and joshing.
Something about the atmosphere on Friday didn't sit well with the macho part of my brain, however. Too many rude jokes and subtly flirty suggestions made in my girlfriend's direction. She was a good three or four beers in front of me. I just became uptight and refused to crack a smile. Minutes later when the group suggested going to a karaoke bar I just refused. I knew I was doing wrong but I just turned into Clint Eastwood and barked aggressively "No!" at any request for us to join the rest on the nightclub crawl.
I took my girlfriend's hand and led her to the bus and, on the way home, voiced my opinion that one mae team leader was flirting with her, I was upset at that and I thought he'd been like that since he'd just recently joined her company. She became upset. I launched into more macho nonsense to justify my meat-headedness and just put my foot in it.
Come Saturday morning I was sorrier than I had ever been - I'd even read about morbid jealousy in college and knew that's what I'd expressed. I knew then, that morning, how much of an overreaction there had been and plead with her that i wished I could take it all back. She just calmly said "Well, maybe we keep you and my work separate from now on." Something that hurt me - probably not as much as I'd hurt her.
We were back on semi-normal speaking/hugging terms yesterday, but I've done a lot of damage to what was our comfy little world. It's just that we did most things together and part of me, on Friday, thought I was crashing some private party and that she was having a far better time with her colleagues than she ever had had with me.
Part of me still believes she was and I need to hush that.
Does anyone have any advice? What can I do to fix things? I need an objective view, but I know I deserve a few beatings.

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