How can I get him to like me?

Okay, so I might sound abit snobby and stuck up but here goes. This guy 'used to' fancy me, we would talk to eachother all the time but I didn't like him. I'm going to be honest but he was abit of a nerd but halarious. So he stopped liking me, because I was just I don't know wasn't trying and he gave up. He now fancies this girl, she is lovely and I want to leave them alone but I can't. I'm the person who cares who they're with and what they look like, but now I don't give a ****. I try speak to him, but he hardly makes an effort now.