Your drinking to the point of inability to keep yourself safe is a serious issue. You could have gotten raped or robbed, this happens to men too (assuming you are a man just due to some details in this post). Or you could have hurt somebody by driving or maybe getting into a fight. The kissing I personally wouldn’t even consider that cheating, if you are giving all the truth in the details about what sexual acts occurred. If I were your gf I wouldn’t give a crap about the kissing and I would want to know about this just so I know I’m with a blackout drunk. She may already know this though. I honestly wouldn’t see it as a betrayal if you didn’t mention this kissing and I found out twenty years later.

See how people have wildly different ideas of what cheating is? This is why you should probably be honest with your GF about this. If you don’t already know her stance on cheating then this is a good opportunity to find out. I’ve learned the hard way that withholding info about how you are and what you really need only prevents YOU from being happy. You end up with a person you’re not compatible with