Its a "Drinking and Cheating" song. In the beginning, we are committed to someone (dating, married, whatever) and are sitting at the bar, drunk and looking to have a good time... with whoever. We feel something is missing at the moment (the only think that really matters when you're drunk) and we want to get "back to good". Now, everyone knows that the same thing is going through everyone else's mind, it's just not talked about. Yet all the signals are there. Eventually, we slip away with someone. As long as nobody notices, who really does it hurt?
The second verse is right after the fact, and regret sets in. We are now hurt, and possibly hurt the person we are committed to, and maybe even hurt the person we were with. But we don't know how to get back to the way it was before what we did (Back to Good). It was fun at the moment, but there was nothing lasting in it ("you don't own me") and was just meaningless ("in fact it's phony as hell"). Yet, we truly hope in the end that this moment will never come up again, or we will be at a loss to explain ourselves.
But should we have to explain ourselves? Everyone has those cheating feelings. Everyone. How can one person look down on another for breaking down and going farther with those feelings than another? One person stops at flirting, another with a caress, another at a kiss, another... ("everyone hides shades of shame"), yet we have all cheated to some degree. Yet it's all still cheating ("but looking inside we're the same").
Overall, the song is just telling us that everyone is human, and we all eventually go astray. Don't think for a second that everyone else is faultless, and don't put other's down for thier moments of going "too far".