Marriage

So the whole point of this blog is to make me talk about stuff that matters... here goes. My husband and I have been married for almost 3 years. A few months ago, I left, and we were separated for about 6 weeks. We have been back together for about awhile now.
Things were bad when I left. He had to make changes, and he just wasn't. He was drinking a lot (not getting drunk, but having 4-6 beers every day at least), and his temper was getting worse and worse, bordering on being verbally abusive. He has some issues (who doesn't?!), a lot of them are easier to understand if you knew about his childhood (just blame the parents, right?)
Anyways, he hasn't had a drink for over a month, and says it's not hard at all. He is doing counseling, and we are going to do counseling together. He's involved in an Alpha program at church (a class for new Christians) and is working on his relationship with God, and with me.
The problem is, I don't trust him. And I don't know how to start trusting him again. It's like I'm waiting for him to fail, so I can say, "Aha! I told you so! You haven't changed!" He continually asks for my patience, and reminds me that change takes a lifetime, and he is doing the best he can. Which is true.
I think I'm just scared that he is going to go back to the way he was, and I am going to have to make that decision again. Leaving him was hard. And humiliating. And a lot of other things. But I feel like I'm trying to sabotage him... push and push and push, and point out his failures until he snaps or something. Maybe I'm trying to protect myself for if he does let me down. Or maybe I still have a lot of resentment that I haven't dealt with.
I know I love him very much, and am so thankful for the changes I have seen so far... so why am I trying so hard to push him away???