Admittedly, I've got several ideas pushing my mind at the moment - many of them involving smut in semi-public settings, girls getting in over their heads, and skimpy outfits - but there's one that came to mind that can take many different forms. Breaking up with someone is never easy, and there are a lot of ways things could get twisted if one or both parties don't behave like adults. We've all done things we're not proud of in situations like this, and I had a few ideas of how things could go. In the scenarios I'm envisioning, both characters would be college aged or young adults (so between 22-27), and I would be playing the male character, looking for a female to play the female character.
Blackmail: A classic angle. Girl breaks up with guy, but forgets that she's sent him fairly revealing pictures or videos that would certainly look good online...albeit not for her. He could attach her name to them, or just threaten to share them with his friends unless she gets back together with him, or maybe just keeps servicing him sexually at his beck and call, to the point where it starts hampering her ability to live her life freely.
Obsession: One partner might not be willing to accept the fact that it's not happening anymore. The guy could start following her around campus, at her job, talking to her, watching her from a distance, taking photos (much easier to do with the advent of cell phone cameras). Alternatively, the girl could text him obsessively, telling him she'll do anything for him, even confront him at his home, force herself on him...which could lead to a sort of consensual blackmail where the guy finds out he can take advantage of her willingness to do things that she might not have been able to do before...
Going too far: A bit more of a one shot idea, and admittedly a twist that plays into a particular kink of mine. She breaks it off with him, but forgets to take his apartment key (or maybe he makes an extra one, whatever). She goes into the shower one day, and he sneaks in (with friends?) to steal some things, but not her valuables. Instead, they steal her clothes, window blinds, blankets, anything she could possibly cover her body with, so all she's left with is the towel in her bathroom.
Naturally, he could stay behind to take that and run off, too, leaving her completely naked and exposed. Certain hijinks could result from that, but I'd want to find a partner willing to play along to see what we could come up with. Would the boyfriend want to just stay there and use her with his friends? Or find her secret toy stash and leave her with that? Tie her up and take her somewhere? Could be dark, could be light hearted, still thinking this one through.
Something else: There are probably other angles. If you think something would work, lay it on me.
I tend to play dominant characters, and my likes/whatnot are in my sig. I think.