RP plot idea:
Muse A is a part of a boarding school, and is known to be one of a group who 'sleeps around' with [whichever gender; maybe both]. And the groups motto is to get them in bed with full consent, and then leave them the morning after. And the fellow students are aware of the açtivities the group performs, but yet many have still taken a part of their shenanigans, making their "job" easier.
And then a new student, Muse B, joins the school. And rumour gets out in the group that they are a difficult one to get, as they're seemingly not interested in any of them. Then, the group makes a bet with Muse A; get the girl/boy in bed. Muse A accepts.
And thus they befriend Muse B, and while it was only just a ruse at first, Muse A begins to see B as a friend, and later as even more. And they decide to simply drop the bet, and just continue becoming close to B.
Turns out, their growing feelings are reciprocated, and eventually the time comes. However, not long after, Muse B figures out Muse A's original plans, and deems them as a betrayal. And Muse A must convince Muse B that they've changed over the time.