Make a list of possessions or articles of clothing which might remind you of somebody or are associated with a person. Your lover's shirt, ex-room mate's dirty laundry, the baseball belonging to a long-past pet. Books, perhaps. Or pieces of art, which you saw with somebody for the first time, or make you think of them. Even films or music. A favorite hang out.
Write a poem exploring this item and the relationship. Re-discover what reminds you of this person, what compels you to think of them when this item is present. It can be sensual, or harsh, intimate or jarring. Things like these can often catch us off guard, especially with how hard they hit home.
Take a look at I Take Your Shirt to Bed Again by Amy Lennon and write.