The story of Psyche and Eros is the archetype of all romance literature. The characters symbolize the soul (feminine) and body (masculine) wed in a divine love affair.
Psyche is the most beautiful being in all creation, the epitome of womanhood. She even outshines the Goddess of love. Eros is smitten by her beauty and falls in love with her. They are married, but Psyche isn't allowed to see Eros because, she is told, he is a hideous monster. But she falls in love with him anyway because he is so kind and loving. (Beauty and the Beast? Bad boys in modern literature?)
Her sisters convince Psyche that the monster which has seduced her will eventually kill her if she doesn't kill him first. She goes with a weapon and a lamp to sneak up on him and slay the beast, but in the light she sees his true beauty. Eros is angry and flies away. He is imprisoned by his jealous mother. Psyche seeks him and must complete impossible tasks. The last task poisons her (sleep) and Eros must come to her rescue. (Sleeping Beauty? Alpha Males and Billionaires?)
They of course live Happily Ever After or it wouldn't be a romance, right?
From a psychological perspective it is easy to see why these archetypal characters dominate romance literature. They are hardwired in our psyche. It is why women fall in love with heroes and men fall in love with heroines. If our characters don't conform to these archetypes they seem strange and stilted. The hero must, in some way, be Eros and the heroine must be Psyche.
We could just as easily say David and Bathsheba or Romeo and Juliet or Clair Randall and Jamie Fraser. Though Romeo and Juliet is technically a tragedy. But you can name a hundred romances and they would all conform to the Eros and Psyche archetypes, even real life romances. It's who we are, how our heart and soul live as one. We recognize it in literary characters and it touches us, drawing us in, and making us part of the story.
I could write volumes on the emotional and psychological triggers at play, but that isn't important for this post. Look at your characters. Can you see Eros in your male lead? Is your female lead Psyche incarnate? Do they suffer for their love? Do they fight insurmountable obstacles? Do they stand together when the whole world is against them? Do they pull apart, but long to be together?
These are all classic threads in Romance. If your story doesn't have them it is lacking the Heart (Eros) and Soul (Psyche) of romance and readers will feel that.