Couples come in all shapes and sizes.
There seem to be some general categories of couples, and many more than will get listed her. But there are a few types that I see a lot.
One is the clingy couple. I know a few couples who must have 'best' friends. You're either almost living with these people 4 days a week, or you're off their radar altogether. Often the clingy couple will move from one couple to another as their 'best' friend, like Proustian romances. Between break-ups the level of intimacy can become almost familial, again with couples just about living in each others' houses. (This sort of couple makes me want to run a mile.)
Then you have the social couple, who can't do a thing alone. Not clingy in the same way as the clingy couple, but almost completely unable to spend time together alone, as a couple. This sort of couple regularly holidays with other couples. (This really isn't my scene either, holidaying with other couples seems extraordinarily tedious, and hard work.)
Of course you get the usual continuum of co-dependency couples, with different varieties of slavish devotion or Stockholm syndrome.
The childless couple, and yes everything here is a horrible generalisation and there are no pure types, often has dogs that take on the role of the kids. And/or they consume 'culture' - fine dining, concerts, films, stimulating conversation. The childless couple is also often obsessed with the intricacies of their own relationship, or erect various shines to love (like Tuck and Patti, who started out creating music which always surprised and delighted and then degenerated into increasingly saccahrin paeans to "love").
The shopping couple buys things to have something to do together and speak about. Every time the relationship feels a bit stale (maybe once a week), a new gadget appears.
Maybe the couples who finish each others' sentences are some variety of co-dependency, I'm not sure.
Finally you have the couples who are 'best friends'. Lots of those now, the friendship is THE thing, for them. Seems to be arse-end-about, to me.