Jules - I'm really glad you brought this up. It's so helpful to be able to get things out in the open.
For me, it was so much easier to just come out with it. If you feel ready - this might be a good time. The way you describe your friendship, it sounds like you won't be losing her. You could even tell her about those times you felt bad for not being fully present (the times you say you treated her poorly). You can tell her you're not yourself when you drink, and that's one of the reasons it needs to stop. I know I hurt and confused many people when I was out of control. When I was able to unburden myself to some of those people, it was a huge weight lifted off me. Most of them were glad to know it was ok to talk about my problem, too. They'd been walking on eggshells, afraid to say the wrong thing.
Whatever you decide - you have us to confide in and talk it over with. That's what I love about this place.