My favorite love theme in a film score is the "Ship of Fools" love theme by Ernest Gold.
My first exposure to it was the 1965 Oscar cast in early 1966. It was nominated for Best Picture and the scene they showed was one between Oskar Werner and Simone Signoret. That exquisite theme was playing under their scene in her stateroom.
A few days later, my best friend (who was also very much into film music) and I went to a drive-in to see this film. And I later bought the original score recording played by Arthur Fiedler and the Boston Pops. A few years back, I was delighted to buy a CD of the complete origina score on a boutique label.
I once wrote a fan letter to Maestro Gold extolling the virtues of that theme and various other scores of his, including the fact that "Exodus" was the first soundtrack I ever owned.
I received a very nice letter in return from his wife who was writing for him because he'd had a stroke which ended his career. She told me he was very pleased by my words and thanked me for thinking of him.