In the end
Perfect song by Linkin Park to describe anyone who has put effort into something (typically a relationship) where none of it mattered.

A good song to listen to to remind one that the effort was wasted on the wrong person.

Note: the lyrics indicate that one party was genuinely interested in pursuing a relationship but the other party was only in it for the sex.
"I put my trust in you, pushed as far as I could go... But in the end it doesn't really matter"