This is a song from Mann's ambitious concept album The Forgotten Arm, which tells a love story between a girl and a boxer who is addicted to heroin. I rather like the album as a whole--although the nature of the concept album makes pulling isolated songs out from it problematic, to say the least. It's one of the reasons why all those 'rock operas' that were popular in the 70's never quite caught on...much to Styx's chagrin.
It's another example of a song whose sweet, poppy exterior hides a darker meaning--namely that this is a song about her POV character having great trouble coming to grips with her boxer boyfriend's addiction. And make no mistake--I've always thought Aimee Mann is a master (mistress?) of the tension between message and messenger. The melody here is so uplifting and swinging and loving, and yet Aimee is giving voice to a woman who is telling her lover that she Just. Can't. Cope.
I don't think I'm spoiling anything for anyone who might be curious about The Forgotten Arm that the songs that follow this one get darker before the album ends with a very faint ray of light in the last two songs. I do recommend it, althought I'd strongly advise you listen to it at least that first time straight through to get the full impact of what Mann is trying.
Since this song wasn't a single, there's no video...but here's a rather striking scene from Magnolia, which finds the characters of the film channeling her at a particularly dark moment.