A housewife gets raped by a random guy and continues to have sex with him while her husband is away.
Netorare, used to define a genre of Eroge (Hentai Game), meaning "Cuckold". In short, the main protagonist's loved one(s) are taken or seduced away from him and the heroine might be willing or unwilling. This is to cause an emotion of deep jealousy on the viewer.
