I took a grief class after my mom died last year and one of the things we had to do was write a letter to our loved one and share it in group. To me I found it to be cathartic. There were things I never got to say to her when she was alive, things I hadn't forgiven her for etc. It was a painful experience but very worth it. We had to do it in a specific way. It was supposed to include I am sorry for: I forgive you for: and then emotional statements like I love you, I miss you and at the end we had to say goodbye. I am glad I did it. I also did the same for my dad with my therapist when he died. That letter was just any sort of letter, didn't have to be done in any specific way.