Contemporary critics read all sorts of complicated sexualities in Rebecca. Rebecca herself (though she's dead before the novel begins, and never reappears) is sometimes seen as bisexual and sometimes seen as an object of same sex desire. We hear from a variety of sources that Rebecca has unconventional attitudes toward sex, and has multiple affairs, including a long term one with her first cousin Jack Favell. There's some suggestion that her sex life with Maxim is totally non-existent. Similarly, Mrs. de Winter's sex life with Maxim seems to be good on their honeymoon, but then sputters out at Manderley – until, that is, Maxim reveals that he despises Rebecca and murdered her. His confession re-ignites the passion, leaving more than one reader uncomfortable in the process. It's also uncomfortable to know that Rebecca is hated and eventually murdered by her husband because of her sexual activities. Discomfort is what a novel like Rebecca is all about. It's meant to shake up our thinking and make us question or own attitudes and beliefs concerning sex and sexuality, and how it pertains to marriage.
Maxim de Winter is a portrait of a sexually repressed man, whose repressed urges erupt in violence and anger.
Although Rebecca is portrayed as a raging nymphomaniac, we don't have evidence she had sex with anyone but Favell, and even that isn't certain. We need to cut the girl some slack.