Please help me!

First I want to apologize for my english, I’m not very good to write in english.

When I was a child, my mother used drugs (heroin and cocaine) in front of me, I saw and lived things that you can't even imagine, and I'm very traumatized by that.
I live with my boyfriend for about 9 months, we have a very complex story, but we love each other, we know we want to be together forever, but I can't deal with it anymore!
He used to consume drugs, less heroin, he was addicted to weed and since November that he left it, and he says that he doesn't want anything else related to drugs in his life, and I believe him, but I can't stop having his image using cocaine, it’s over and over in my head, and I'm losing my mind, it hurts so much!!
I really don't fucking care about my mother, I tried to help her for over 10 years and she shit in my head so I gave up on her, but my boyfriend is different, I love him more than anything in the world , I want to build a life with him.
We've known each other since we were kids and I've liked him since I met him, but because of some things, we only can be together now, and it hurts so bad to know that he did those things and I feel guilty that I couldn't be there for him, because if I was there none of this would happen.
Last night I saw a guy on a netflix series using cocaine and I automatically imagine my boyfriend and then I started to cry and we fought. I Iocked myself in my room for like 2 hours crying and screaming so badly and my heart and my chest was hurting so much that I could hardly breathe. I can't handle it, I can't stop having that image in my head and it's killing me. Because cocaine is really bad, and I saw things when I lived with my mom and it's really, really bad, and I can't imagine him doing something like that! I'm praying to God all the time that this is just a nightmare.

Please, please, help me.