Griffin and Phoenix
Griffin (Dermot Mulroney) and Phoenix (Amanda Peet) are both dying of cancer when they begin a relationship. They make a promise to each other that when one of them is truly dying and must go to the hospital, the other will leave so that their last memories of each other won't of their suffering.
Phoenix is the first to become deathly ill, and she leaves Griffin a note saying goodbye. He comes to the hospital and tells her he lied and that he intends to stay. He steals her out of the hospital for a day and takes her to the forest where he has set up an early Christmas tree for her as she will not live to see December, and they share their one and only Christmas together.
Thanks Mary C!