The story Conflicted is a very good start. Good corruption without the need for blackmail, drugs, lying or other dubious consent stuff. Compared to it though, I'd have a slower start with more seduction. There'd be more emphasis on the bullying, but it wouldn't go to ridiculous extremes (I feel Conflicted kinda jumped the shark right at the end on that front). The mom would eventually see the bullying and betrayal as a guilty pleasure, as long as it doesn't go too far. As in that story it would be based on the mom trying to get the bully to stop being physically abusive and start messing with him in other ways, that she would also join in on eventually. Also, I don't really care if there's a husband in the picture or not. I'd also make it first-person narration (the mom) for sure, I think it could really add to the corruption aspect.