Force yourself to make a different choice for a short time, for at least an hour. Do something physically hard that, under different circumstances, you can easily do and that you usually enjoy, perhaps a brisk walk or a short hard run. If you can do it with a good friend who is not overly sympathetic, so much the better. While you are walking or running, especially with a friend, you will notice you are not depressing. For a short time, you are not thinking about your unhappy relationship, and you feel much better. But as soon as you finish, you tend to go back to thinking about the relationship that has gone bad, and the feeling comes back. To depress, you have to keep thinking the unhappy thoughts. To stop these thoughts, change what you want or change your behavior. There is no other way.
William Glasser, Choice Theory