In my view, relationship movies never get old because humanity will never not be confounded by their relationships.
I think a lot of people, especially women, feel like to be whole, you need to find part of yourself in another person - probably because of the fables we're told as kids.
In most movies there is a Prince Charming who rides up and saves the girl.
The secret to a long-lasting relationship is perpetually imagining the worst. It's a world view tracing back to my Eastern European ancestry and one I draw upon regularly.