Well, it's sung by a female singer, so perhaps a lesbian love? I mean, maybe being bay myself makes me a little bias, but it sounds a lot like a love song from one woman to another.

I'd say the song is about the way people's feelings have a tendency to change over time. I've been in a situation like this song, pining for a girl for weeks, months, and when she finally was ready for a relationship with another girl, I was taken. Her loss, not mine.