Mick Jagger has posted a poignant tribute on Facebook to his late companion, L’Wren Scott, saying he is still struggling to understand her death and will never forget her.The rock star canceled a concert in Australia to fly to New York in the wake of Scott’s death, said the couple had spent many wonderful years together.Calling Scott his “lover and best friend,” he paid tribute to her talent as a designer, and what he called her “great presence.”He ended his message by saying: “I will never forget her.”Scott, a noted fashion designer, died on Monday of an apparent suicide.