I don't know that you should stop thinking about it...definitely don't try to make yourself stop thinking about it if you can't help it from coming into your head as that will most likely have the opposite effect.

To me, it sounds like you still have something inside of you that needs to work its way out. You seem to still be in a lot of pain over what happened. Did you ever have a chance to tell that person what their actions did to you? Even if you never get to say it to them, writing a letter and putting every bit of emotion that it stirs up into your writing could help. Yeah, it might be triggering and you'll probably feel a bit hung over afterward for a while, but the point is to get all of that out of you internally and down onto the piece of paper. And if you need someone to hear it, we are all here for you.

If you aren't much of a writer, the "Draw Your Scar" exercise could be good. Draw what it looks like and where it would be on your body. It helps seeing mental injuries as physical ones for some reason. And seeing it physically could be what you need to initiate the next step in the healing process.

Just my two cents. These could work, or they could make things worse. Just something to maybe try, I guess.