Oppressive governments are always fun, but a game based highly on sex would get weird to role play. I don't quite see how a government can enforce this without spending ridicules amounts of gold on magical means. And finally why would the government do this exactly, with both parties staying with their partners and more importantly being able to choose their partners would not oppresse the people but partially empower them. Maybe if the two parties were those who never got to have intercourse and those who were forced to breed w/o choice of partner and not the same partner, that might make the government more oppresive and the setting less weird to RP.