As far as literary couples, I'm crazy about Percy and Mary Shelley. Mind you, Percy cheated on his first wife (who later committed suicide), but his poetry was filled with romantic longing. He encouraged his second wife, Mary, to write and inspired her novel, Frankenstein. After his short life (he drown in a boating accident while on vacation), Mary still loved him dearly and held a candle for him until the day she died.
There are so few enduring couples in entertainment, but a few stood the test of time. One of my favorite couples was Johnny Cash and June Carter Cash. They were married 35 years, and Johnny was holding her hand when she died. He credited her for keeping him off drugs.
In history, I adore George and Martha Washington. They endured despite their struggles through war and politics. Martha kept all of the letters her husband wrote her and burned them before her death rather than letting anyone see their private words. I'd love to read them, but I understand her wanting to keep his memory to herself.
I think what makes these couples work is that they understood each other so well, and there was a perfect balance of give and take. If there is too much of one person doing all the giving or taking, the relationship is doomed. No competition here, just encouragement. A partnership. Now that's romantic!