Is it normal to have sex with a guy but be straight?

Uh, yeah, if you were drunk, than it really doesn't matter. Even if you were sober, there's nothing wrong with trying and exploring things.

You just have bisexual tendencies.
That's all. Nothing to be ashamed of, really.

Yeah, it's very normal. You don't have to be concerned about being gay, straight, or bi. These are just society conventions, trying to name abstract thing which is the desire. You just have to do what you want, maybe you got atracted by another guy, maybe not. And maybe you would have sex with your friend again, which is great... Or maybe just not. For me, this is not cheating, actually. Come on, we're in 2012, just let your desires guide you by your life and be happy. The fact of being drunk doesn't change anything either... Hope you explore your sexualty! Bye.

its ok just enjoy it

Bazwell if that was not a copy and paste, then PROPS!

I initially agreed with Johnny592 that this is nothing to be ashamed of, then I remembered that you have a girlfriend and cheated on her, but were more worried about your sexual orientation than the violation of the exclusivity she probably holds you to.

I would recommend the movie Humpday (http://www.imdb.com/title/tt1334537/) as an exercise in the trials of drunken folly, the silliness of mindless testostorony selfishness and the inextricably awkward nature of relationships, sex and sexuality.

That said, I personally believe that those who when intoxicated, act in ways that they would later decry when sober, are ultimately in denial. The presence of mind it takes to commit an act and to continue with each step of the act...all the way to completion: this is will, this is deliberation, this is decision! All the alcohol (or other drug) does is remove the inhibition of morality/ethics/logic/indoctrination etc, and make the unconscious a bit more accessible.

Whatever the frame of mind, the energy and gusto it would have to take for a male to have sex with a friend suggests some sexual attraction to this friend or perhaps to males in general; whether this male realizes or would admit to it or not, is enormous. We're talking sneaking off to a secluded destination, foreplay or whatever it takes to get the mood going, getting and staying erect
throughout the act, having time for happy endings etc. This all yells DECISION(!) to me!

I would encourage you to reflect upon this, perhaps even see a counselor to flesh out all that you have been dealing with since this incident. You might also want to pay some attention to the self-medication with alcohol as this is very relevant as well. Then determine if your girlfriend deserves the treatment she is receiving from you and what kind of person makes that kind of determination about a loved one.

best of luck to you!