A Wife's Suspicions

Her abusive stepfather was murdered. So was her womanizing boyfriend, who used to beat her. She became the prime suspect. Many men are afraid to marry her in case they end up dead at her hands. Yet she gets married, to a husband who offers her a platonic kind of love. Though they have no physical intimacy, he is considerate and kind to her. She can't shake the feeling that he's hiding something, and suspects he has another woman.

A murderer appears, claiming women as his own before killing them. She doesn't think it could be her husband, because she believes he's impotent.

Who is the killer? What is her husband hiding from her?