[still]

Lyrics should be left to intrepretation but if you're looking for what the meaning was behind the song...

The song is written by a guy in love. He's in love with this girl, cannot understand why, but he's trying to convince her to come with him, saying he's rich, forget about it, he's not going to lock the door behind her, she's free to go, he just wants to be with her. She takes off, too immature to deal with what's in front of her. Fast forward, he gets engaged to his longtime girlfriend but he still cannot get this beautiful, funny, albeit stupid girl out of his head. That's why 'the rules of engagement are hard to endorse'. He's still trying to resolve things regarding this other girl, but he seems to keep breaking those secret rules of 'engagement'. And this stupid girl just isn't ready for him.

Him, here now no! It's about a time he caught this girl having a really regrettable indiscretion with a friend of his. There, that's the story behind it.

...and you wrote the song,correct?

No but I have first hand knowledge of the actual story behind the song. But you should always take away from it what you interpret.