mourn for (one)
To experience grief over one's death. Don't mourn for me, sweetheart—I've lived a good, long life, and now it is my time to go. She was still mourning for her husband when her mother passed away from a stroke.
mourn for someone or something
and mourn over someone or somethingto grieve for someone or something. Everyone will mourn for you when you go. We all mourned over the end of the holiday. There is no point in mourning over your cat. It won't come back.