Lust and Madness and Murder Oh My! [Ex, NC-H, or NC-E]

[The Great Triangle]

An idea for a game I've been itching to play:

A lover is in love with his or her beloved, who is herself attracted to a third person, a victim.  The lover, desperate for the undivided affections of his beloved, seduces him or her and gradually drives the beloved insane, turning her into a mad wretch heavily influenced by her lover.

The lover and the beloved, now both quite mad, kidnap the victim and kill the poor person, laughing as they do so.  A few hours later, they realize what they have done, and coil into a self destructive spiral of love and hate, running from their own guilt, and from justice, to escape from a crime they may not even have actually committed.

I'm pretty flexible about the specific setting and character identities, and would be happy with any of the roles except the victim.   I can also help brainstorm setting details for the story, which I intend to not be terribly long.