Multiple Partners, Polyamory, Harem, Coven, etc.
Assume it'll have smut.
Daphne's Letter from the Future - TomHRichardson
Harry Slays Voldemort - StevenTLawson
Hermione deals with this - Chubster23
Two Minds, One Wand - RobWilsonWriting
Whore Class - Riotstarter1214
A Vow of Control - MayorHagger