In keeping with Valentine's Day - who is my favorite fictional couple?
I've probably had dozens over the years, as a teenager I read a pretty diverse mix of books from the classics to science fiction (which, if they featured women at all, they made them male sex fantasies) to fantasy (Tolkien's mentioned Arwen only briefly, but Eowyn was stellar) and a few standard romances (which were pretty unrealistic prince/millionaire types). The old classical writers knew a relationship was essential to a story - Anne, Constance, and Milady De Winter were essential to The Musketeers. Later novels seemed to lose some of that. (George R. R. notwithstanding - he wanted to show the abuse of women of a given time period, and went a little overboard.)
Fortunately, the depictions of relationships grew and improved.
F'lar and Lessa from Anne McCaffrey's Dragonrider series, a realistic depiction of a relationship with the inevitable ups, downs and conflict. It was the first time I'd seen relationships portrayed that way by a popular fantasy author.
Chelsea Quinn Yarbro's vampire Saint Germain and his relationships, especially his love/friendship with Madeline de Montalia, is another great couple. In romance novels, Cameron Quinn and Anna Spinelli - no alpha, just a relationship balancing careers, responsibilities, and life - from Nora Roberts Chesapeake Bay books, as well and Eve and Roarke from the J. D. Robb books.
In my own writing, I tend to prefer relationships/couples as an essential part of any story - each is different, some are intense, some are more low key.