He said he "dosen't know if he cheated or not"?

Me and my boyfriend had broken up because he needed his space and we tried to stay friends. I'd talked to one of his ex's and found out that she had sex with him several times while me and him were dating. He tried to deny to her that me and him had ever dated and that we ever had sex. Then when I talked to him I asked him if he had cheated. He said he doesn't know if he cheated on me to which I replied "What do you mean you don't know? Do you know how stupid that sounds?" Then he said "Well remember when you were on all those drugs and you said you don't remember anything? Doesn't that sound really stupid? Drugs don't make you forget anything."

I cannot tell you how how much this hurt me. A few years ago I went through horrible addiction problems and I over dosed four times. 90% of the time I didn't know what was going on. It's like there's this big chunk of my life missing. But I got myself off all the drugs without help from anyone, I did it all by myself. I've been sober for 9 months. I've never been so proud of anything in my life and I feel like his one comment just crushed everything I've worked so hard for. How can being an addict make me just as bad as him? All the stress makes me want to go back to my old life and that scares me.

I feel so used, lied to, scared and stressed, and I don't know where to go. He wants us to still be friend and hang out but I don't know. I just feel so lost.