Depending how far apart the couple is.... planes, trains, other types of transportation.
Letters (the old fashioned kind with stamps and air mail stickers). A telephone cord with the couple at either end. For the really far-flung: a passport, stamped with the destination where the couple will finally be together. Maybe a dove could "deliver the mail"? Or a carrier pigeon, or a snowy owl, or whatever kind of bird would work.
A heart in two pieces like a jigsaw puzzle, that would fit together if they were placed closer together, but actually on opposite ends or different tiers.
More of a novelty idea: a large carton plastered in stamps and airmail stickers, with one person popping out of it.
gaaaa now I'm gonna lay awake half the night thinking of more ideas....