I found an essay on how to know when one is done with therapy.

As often as people ask a question about how to begin therapy, folks don’t seem to ask how they will know it’s time to call it quits. Psychotherapy involves a relationship between two people and ending any social or professional relationship can be difficult. Therapists are trained to know how to successfully end a therapeutic relationship in a healthy, positive manner. Despite their training, however, sometimes the therapist doesn’t know exactly when to end therapy. This article is meant to help you understand and learn to look for the signs of when it may be time to end your therapy.

From Knowing When to Call it Quits in Psychotherapy, by Dr. Grohol, author of Psych Central.

I would like to add that therapy is not necessarily a once-in-a-lifetime treatment. Just as one might catch pneumonia several times in one’s life and need to see a physician then, one may periodically seek therapy to help with life problems.