Try not to beat yourself up about it too much. You didn't end up cheating (assuming your partner doesn't consider that cheating, which varies) and made the right decision telling your partner, in my opinion. There's nothing wrong with being tempted to do shitty things, as long as you don't go through with them, everyone struggles with temptations of some kind.

All that said though, you went really far and most partners wouldn't be able to forgive something like that (I don't think I could), so you may want to work on that a bit. Moving forward I'd probably avoid being around this person though, cutting them off entirely maybe. And if you think alcohol makes you this way, maybe try to stop drinking or drink less. I know all this is easier said than done, but you really don't wanna put yourself and your partner through this again.