Honestly, if he was sober, then he'd be up there on your scale of disgusting. However, him being drunk does make a difference. While, in whatever case it may be, the situation is bad, he didn't do anything against her will. From your post I understand that both of them were intoxicated, and if either of them were sober that would never have happened. While it doesn't take the blame away from either of them, you can't blame the guy without also blaming the girl.
Now, that's not exactly your question; the question was how bad is the guy's mindset. And, honestly, at some level of intoxication the mindset almost goes out the window. Some people have better control over it than others (you seem to have rather spectacular control), but his mindset while drunk is likely completely and totally different than that while sober. In that case, you need to base the mindset off of what he does in his 'normal state', so to speak. What I mean is, if he's constantly getting drunk and cheating on people while doing so, you can judge him by that. But if this is a one time thing, and he feels bad about it too, you can't judge his entire mindset off of that one incident; just because he made a mistake doesn't mean he's a douchebag who completely disrespects women on all levels, much like just because it happened once to the girl doesn't mean she's a cheating whore who'll sleep with anyone, ya know?
Now, your third edit complicates things that much more. If this were just a friend, there would be reason to be angry at the guy, but at the same time it was the girl's fault as much as it was his, and you'd have to take that in to account. It's more complicated, but largely the same, in this case; it's both their faults. And, possibly more importantly, it wasn't the guy that cheated. From the point of view of an observer, I don't think you can be mad at the guy if you're not mad at the girl, and even then it makes more sense to be much more mad at the girl, since she was the one that did the betraying. However, from the point of view of the one being cheated on, if it happened to me I likely wouldn't mind seeing that guy lying broken and bloodied in a back alley somewhere. I might even be the one to do it, given the opportunity. I'd also really, really want to forgive the girl, and likely would in that particular case (being drunk isn't an excuse, but it might be justification for a second chance). If it happened again though, I don't think I'd be able to forgive her.
I apologize for not sticking with your initial question, but it's hard to pass judgement on the guy without also doing so on the girl, because both were instrumental in what happened and without one you can't fairly address the other.
Now, that's not exactly your question; the question was how bad is the guy's mindset. And, honestly, at some level of intoxication the mindset almost goes out the window. Some people have better control over it than others (you seem to have rather spectacular control), but his mindset while drunk is likely completely and totally different than that while sober. In that case, you need to base the mindset off of what he does in his 'normal state', so to speak. What I mean is, if he's constantly getting drunk and cheating on people while doing so, you can judge him by that. But if this is a one time thing, and he feels bad about it too, you can't judge his entire mindset off of that one incident; just because he made a mistake doesn't mean he's a douchebag who completely disrespects women on all levels, much like just because it happened once to the girl doesn't mean she's a cheating whore who'll sleep with anyone, ya know?
Now, your third edit complicates things that much more. If this were just a friend, there would be reason to be angry at the guy, but at the same time it was the girl's fault as much as it was his, and you'd have to take that in to account. It's more complicated, but largely the same, in this case; it's both their faults. And, possibly more importantly, it wasn't the guy that cheated. From the point of view of an observer, I don't think you can be mad at the guy if you're not mad at the girl, and even then it makes more sense to be much more mad at the girl, since she was the one that did the betraying. However, from the point of view of the one being cheated on, if it happened to me I likely wouldn't mind seeing that guy lying broken and bloodied in a back alley somewhere. I might even be the one to do it, given the opportunity. I'd also really, really want to forgive the girl, and likely would in that particular case (being drunk isn't an excuse, but it might be justification for a second chance). If it happened again though, I don't think I'd be able to forgive her.
I apologize for not sticking with your initial question, but it's hard to pass judgement on the guy without also doing so on the girl, because both were instrumental in what happened and without one you can't fairly address the other.