Don't feel like a fool. All of us at one point in time (at least I think I can say this) wanted our relationships to work out and believed the alcoholic when they said that they were doing this and that. We had hope that we weren't wrong in our assessment that this person wasn't a horrible and/or sick person but someone like the one that we met and fell in love with. That they had good qualities and continue to have good qualities. And then we are let down.
You left once. You can do it again. I left my AH once and kicked him out once and both times we got back together. He started drinking and using again in August and told me this past Monday that he is, again, done. Since he always says that and it never seems to stick, I am waiting for the other shoe to drop although not getting anxious about it this time. If it happens, it happens. I have no control over him but I can kick him out again.
Stay here. Stay strong. Keep posting. You can do it! You aren't a fool. You are a human being. Don't beat yourself up.