Sometimes there are reasons why someone does not remember something that has happened to them.

I know stuff happened to me from my Ex boyfriend, because I wrote it down but I can't remember it and it's frustrating.

Memories come when we are ready to deal with them.
The more you try to force it out the more you will be pushing it back further in your mind.

Talking about it, what you feel happened, or what you remember can help though.