Lyric discussion by Southbound 

Cover art for Independence Day lyrics by Brave Saint Saturn

Constip8d, he's talking about this person in present tense.

You're biting your lip now, I know 'cause you do it all the time. You're blinking your eyes hard, I know 'cause you used to be mine.

I do know the real-life story. Though it was mutual, it really broke him up that his still-best-friend wouldn't even call him up anymore. In Enamel he talks about the bitterness and anger he felt because of it.

[On the bright side, though Reese would go on to go through another engagement that was broken off (post "Anastasia"), he is now happily married to a woman named Amy :) ]