The play’s two characters are a man and a woman who exchange letters, but not marriage vows, in a warm and complicated friendship lasting 50 years. Melissa and Andy read their own letters as if still writing them and then listen to each-other as though hearing a voice in the distance. “Love Letters” is a tender, tragi-comic and an intriguing examination of the shared nostalgia, missed opportunities, and deep closeness of two lifelong friends.