Benjamin issues (no, not the GFF one)

It's the lack of closure that's bothering you. I'm guessing you never got a chance to properly respond to his accusations, and thus never got to confront any of those feelings of betrayal. I'd almost suggest looking up his number and calling him for the sole purpose of telling him off, but that's more than a little spiteful.

Maybe you just need to work on convincing yourself that your youthful perceptions were flawed, and that he was a lot more of an asshole than you took him for? Someone who has misplaced notions of accountability and buries his problems in drugs obviously isn't somebody you ever want to be attached to. The thing about infatuation is that it tends to blind you to the more negative aspects of a person. He was probably kind of a jerk all along, but you were too smitten to notice.

Jam it back in, in the dark.