I used to combat this and constantly relapse due to thinking I had it under control, hadn't drank in a while, and having one with friends wouldn't kill me...
When I went to rehab, one of the things that helped me most was learning it wasn't an issue of willpower, but that alcoholics are physiologically different from others. There's a chemical imbalance that causes even a little alcohol to activate an insatiable craving that causes us to drink until we're basically unconscious, and then some.
If you have a problem, you can't "just have 1 or 2"- you have to stop entirely. Even if you manage just 1 that first time, it's going to set off a craving to lead you back down the path of ruin, you'll slowly increase each time because "hey, I was fine with just a couple last time", and so on.