Explore the notion of past and present in "Before You Were Mine."
This is an interesting question. One of the first ways the "notion" of past and present relate is through a confusion of times in the poem. Look at the first line. Is the narrator looking forward ten years, to a time when she's going to do this? Is time a metaphor—she's emotionally distant from that interaction, and so it feels like ten years? Or is she, most simply, looking back on that time? This confusion continues in the second stanza. How can anyone not be here yet? You're always "here" in the sense of being where you are.
After that, I'd say that the past and present relate in two major ways, but that they aren't really an instance of contrasting. They are more interwoven. First, the past is always wound around the present, so that they can't really be separated. Second, in the speaker's loved one, the love is always present, like a mystical force, even before they met.