I sometimes think people (both genders) sort of stop putting effort into keeping their relationship alive after they've moved in and/or gotten married. First time's always brilliant, but sort of as if they've reached their goal: a relationship, then 'sag' on the settee and stop tucking their tummies in, burp during and after dinner etc. Figuratively of course. but that kind of feel. Almost taking each other for granted. And I think this sometimes happens real fast.
If ppl kept treating each other as if they were still dating, divorce rates might actually drop.