Who gives a shit whether this song is about a man or not? I can relate to it without thinking of a dude (just change the "him" to "her", there you go - the same goes for Thinkin Bout You). Sexual orientation shouldn't matter anyway, everybody has experienced unrequited love.
While this is probably about being in love with a straight man, I think the true beauty with this song lies in the fact that it’s open for more interpretations. It doesn’t have to be about being gay/straight, or about love. It can also be about not being accepted for who you truly are, no matter what reason