I know it became a big deal to you. But it is in the past. Start with friendship. I am only saying from experience, but, even this can turn out to be more, and not work out.
I'm sorry about the pills interfering. But it may or may not be what you need, depending on how depressed you are feeling. I don't know, I don't want to be on medication either.

I think you should try to accept yourself. I know also about the imaginings of my ex with his girlfriends. I'm sure more than one while we were married, that I found out about later. It destroyed my ability to have confidence, and yes, to satisfy myself because it hurt me. I don't have advice on that. Except, maybe, to use your imagination for the better things... anything, doesn't have to be about sex. Could be a dream of a goal of yours related to school. A dream of the kind of woman you would like to meet, make up a story in your mind. Nothing wrong with fantasy