Any advice to someone with an alcoholic?

So I have been with this guy 12 years of my life. I am 28 he’s 27. We met in high school. So for the last 5 years he’s become an alcoholic and it makes me so sad. Unfortunately with the alcohol problem he became a jerk. He started getting drunk behind my back and coming home all messed up. When he would come home he’d call me names. He even told me he wished I was dead which hurt to the core. He would tell me he didn’t wanna be with me. He never wanted to be around me. I blamed it on the alcohol, but it still hurt. Recently I left him I took my stuff and moved out with my mom. I was there for a month. Moved back in with him because I took him back. Apparently he hasn’t drank now he says that I scared him. Lately he’s got this thought that I’ve been messing around with this guy at work, and I am not. I also think he went through my phone ( I have nothing to hide). I feel he’s trying to catch me on something to take the spotlight off of him. He’s been really nice now which weirds me out because it’s been a long time since he’s been this nice. Also I’m still scared it’s going to happen again. I feel like I have flashbacks of him drunk and calling me names and of the things I went through. I also feel I can’t be genuinely happy because I’m all paranoid he’s going to drink and act like an ass. I’m so confused and lost. Please don’t call me stupid for taking him back. Do you guys think I made the wrong decision? Any advice? Also thanks for any advice.