Personally I’ve always thought that he’s talking about a guy who isn’t into him, but is very interested in someone else. Or the guy used to be interested but faded (you said it looks better on me than it did you) and got interested in another person. All the while, the one singing was always interested in him. His feelings never faded. And so he’s jealous and wishes he was the girl the guy is now interested in (I wish I were Heather).
Personally I’ve always thought that he’s talking about a guy who isn’t into him, but is very interested in someone else. Or the guy used to be interested but faded (you said it looks better on me than it did you) and got interested in another person. All the while, the one singing was always interested in him. His feelings never faded. And so he’s jealous and wishes he was the girl the guy is now interested in (I wish I were Heather).