I think you're looking at this in kinda the wrong way, not that I blame you, I understand the obsession with wanting to know exactly hat happened. The thing is though, you might never really know exactly what happened.
The more important thing is that something happened to you. If I were you, I try not to worry too much (easier said than done I know) about what exactly happened, and focus more on what effect it has had on you, and try and heal from those effects. You don't need to know exactly what it was in order to start healing from it.
I also think many of the comments in this thread regarding your parents possibly being in denial and being manipulative of you have some validity. I would suggest at least taking a break from having contact with them, and see if you feel differently about these things in a few months. My gut instinct says once you arent hearing the things they say on a regular basis the light of clarity will start to shine a bit more for you and the who/what/where/when/why stuff will work itself out in time if you just deal with the effect that whatever it was that happened has had on you.
My mom molested me. I don't actually remember the molestation itself, but I remember lots of inappropriate behavior, I know she was sexually active with my brother, and I can tell from the couple times I have tried to be intimate with women that certain things gave me emotional flashbacks while other things were just generally anxiety inducing. Even apart from all that, I just KNOW. Its hard to explain, but I think I am aware of those memories on some level, even though I can't actually consciously remember them. While I was still in contact with my parents though, I could never trust myself to know truth from confusion because I was constantly hearing the manipulative things they would say on a regular basis, and believing
in my gut instincts was complicated because it was all tied up in a desire to believe that couldn't possibly of done those things, they loved me, etc, because I just wanted that stuff to be true so badly.
I am starting to think that someone else did this to me, but that I somehow super-imposed my stepfather's face onto the perpetrators. It is INSANE, CRAZY, that I will probably never know who did this to me.
Have you ever heard of Occam's razor? Its a theory that states the simplest explanation has the greatest chance of being the correct one. The 'razor' part is about cutting away unnecessary complicating things from an explanation. Lets apply that to your idea you superimposed your stepfathers face onto the memory of another person abusing you. Why would you do that? It doesn't make any sense. It might make some sense that if your stepfather abused you your mind would want to believe it was a stranger because that would be less traumatic than it being someone who was supposed to protect you. The simplest explanation for that memory is that it was correct, your step father did take part in abuse, and your parents have an interest in denying it. I'm not saying thats absolutely the truth, but its the simplest explanation and I think has the greatest chance of being the truth.
Regardless, something happened to you, and your parents seem more interested in proving their innocence than in providing comfort security or healing for you, which is sad.
