self-forgiving for questionable cheating

I don´t ever take drugs, but on a night out over a month and a half ago, while exceptionally drunk, a guy from my college course gave me some ecstasy and I took it. This is out of character for me. I completely blacked out which is also something that never happened to me before but have a vague recollection of panicking and telling someone a traumatic sexual harrassment incident which happened me in the past but which I usually keep quiet. I remember pulling apart from the guy for a kiss (the guy who gave me the pill) and had been confused because it wasn´t the way my boyfriend kissed me and wasnt a tongue kiss. Then apparently I went over to one of my friends and told her that the guy I kissed who I named as my boyfriend I was going to marry and I loved him loads. This is all from other peoples information apparently. So moving on, the next day I remember, feel awful and tell my boyfriend. He was back from a night out when I told him and was drunk and angry and then when he was sober, the next day immediately forgave me and said he knew it wasnt me and that I would never cheat on him. I genuinely would never cheat on him I love him with all of my heart and hurting him was the worst thing ive ever done. However, I just cant forgive myself. I know I thought it was my boyfriend, there was no intent of cheating or attraction to the other guy I dont care about him at all, but I cant stop beating myself up about it. Ive spoken to a counsellor and that helped a bit, and Ive promised Im never touching drugs again, Ive done everything I can possibly think of to rectify the situation- asking people what happened, telling my boyfriend the truth and buying him a gift to apologise but I cant get over this im so disgusted with myself. How do I learn to forgive myself and move on because I dont want this getting in the way of things between me and him and I feel bad when I bring it up and apologise again? please please help