Well, you've got yourself to blame then, don't you? If you go around throwing punches, you're asking to get your ass kicked.
You let your emotions get the better of you, and you paid the price. Hopefully, you learned your lesson, but it doesn't sound like it.
I've been going to concerts for about 24 years now, and have never, EVER had a problem. Most security types are pretty cool people if you don't fuck with them.... And believe me, I used to go to shows at Harpo's in Detroit. THAT was one rough place. Hell, I was front row for Testament when James was playing with them there. (he never did throw me a pick.)
Now, if the guy was really fucking with your girlfriend, (I can't be certain by your wording... DID or DIDN'T he slap your girlfriend's ass?) there are several smarter ways to get even.
#1) Call the police and have your girlfriend tell them that the security guard in question grabbed her breasts in an inappropriate and sexual manner. It doesn't matter if he did or not. He's gonna have a very bad day when the cops get a hold of him.
#2) Wait till after the show, find his car and license plate number, and call it in as "driving erratically, possibly intoxicated." For an added bonus, throw in that you "might" have seen that he had a pistol tucked under his belt. Guaranteed a "guns drawn takedown' will occur.
Remember: "Don't get mad. Get even."