Why do you humans care about love and relationships so much?

Same reason we eat and sleep. It's pre-programmed and like a plant without water we wither and die inside if we have no one to interact with and share deep meaningful relationships.

We also learn from interactions.

Humans are by nature social creatures. Our biological programming is primarily designed for reproduction and the facilitation of offspring. Our societies have become so difficult and cumbersome and filled with financial peril that it's safer to pair bond with another human so you've got double the income and at least one fallback should a job loss occur.