>>716461000
Well, it looks like you got the hard part of creating a compelling backstory down already.
Have the VN take place entirely in the present, with the MC trying to deal with this weird girl that's suddenly coming onto her out of nowhere while reminiscing about the girl he was friends with when he was a kid. Then it builds up to the big reveal that she was the girl from the MC's childhood this whole time.
(Also, I'd recommend cutting out the molestation part. You'll likely get plenty of people accusing you of adding it in for sympathy bait, or calling her a used goods whore)