Communication and respect. If something bothers us we talk about it even if it is difficult. Respect - I work for someone who says terrible things about her husband and relates things she has said to him that are horrible.
I would never talk to my husband that way, nor would he talk to me like that. It is common courtesy if you love someone as much as a husband and wife should love each other, that you treat each other with respect and treat them as if they are precious to you.
It also helps that we share our common faith.