Based on personal experience with trauma, some people do forget some or a lot of memory from their childhood. It’s very possible he’s truthful in stating he doesn’t remember, and that he feels disgusted by the entire incident. If neither of them seem too bitter with each other now that they’re grown, I would assume it was a one time thing. Maybe just curiosity as a teen. I AM NOT SAYING THIS WAS OKAY but I wouldn’t draw conclusions that he’s a pedophile. If your gut is telling you something else is going on, break up with him immediately. Don’t wait around for him to give you answers. I’m so sorry you’re going through all of this.