Well Cran Apple, glad you have joined in. Marriage is not exclusively about sex and you aren´t wrong in pointing this out but it is the norm in most that a man and a woman do have sex as the most intimate physical expression of their mutual love and pleasure in each other. It is definitely not the be-all-and end all of the relationship. Mutual trust and a common aim would be paramount for me. Companionship and mutual assistance too. 

Anything you want to define otherwise would be a very good friendship, perhaps? I know quite a few (mainly female) couples who live together for company´s sake and I don´t see this as wrong. But when a man and a woman wish to live together for the rest of their lives and build a family then sex has to happen and that is the real definition of marriage in every culture, not just the christian culture which we know best. But I´d love to hear other submits on this. Thanks Cran.