There should be another word for this feeling—a sort of sorrowful happiness, or a happiness that only deepens someone’s sorrow. The closest I can come to it is the Portuguese word saudade, which nears this feeling but tempers it with nostalgia, a wish for something that was and can never be again. A grieving person lives in a permanent state of saudade, but saudade does not incorporate joy. And grief might be simpler if joy never tried to intrude.