Be sexy without being over the top. You don't want him to get too excited and seek another inmate for comfort. Be subtle. Be sure to give lots of positive reinforcement for the good things he is doing or has done!
Hello My Dear,
How is your life there? I got your letter yesterday I am fine here. The only sadness is that you are not with me. I am eagerly waiting here for you. I miss you very much. I always think about our past rememberence. I love you darling.
Wake up. Are you sure you want to write love letters to somebody in jail? You are living in dreams, not in reality. Tell him you need somebody you can rely on. No drama. No chaos. No rule breaking. That might be the best love you can give him.