If you want the motivation back, you must feed it. Feed it everything. Books, television, movies, paintings, stage plays, real-life experience. Sometimes feeding simply means working, working through nonmotivation, working even when you hate it.
Dear Asshole: Thank you for keeping your word and believing me. It was more than I expected. Also, I'm sorry you were inconvenienced by my gluing your locker shut at the beginning of this year. However, I am not sorry that I did it, because it was a lot of fun. Love, Alex.