I threw a plate at my girlfriend.

I'm under a lot of stress right now, and I'm recovering from a heroin addiction. I've been best friends with my girlfriend since the 5th grade. Almost all her boyfriends before me have been abusive in one way or another I promised her I'd never hurt her. I don't know what hit me but we were having a stupid argument in the kitchen, she started walking away and I just picked up a plate sitting on the counter and threw it at her. Luckily, she ducked and it missed her. I don't know what came over me but I feel horrible and I don't know what to do. Also, about a week ago we were having a small argument and I almost hit her I was about to then I realized what I was doing and I didn't. Advice?
I threw a plate at my girlfriend.
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