Ginny and Colin both once had a crush on Harry Potter. They don't even try to deny it any more, when their friends tease them. It was very different for each of them, though.

Ginny wanted to be Harry's girlfriend. It hurt her for a long time that he only saw her as Ron's little sister, someone to be protected when necessary but otherwise ignored. She's got over it now, and they're friends.

Colin, on the other hand, just wanted to be Harry for a long time. It took a realisation that Harry's life wasn't perfect to make him grow up. He's got over it now, and is living his own life.

After all, they've both found something better.