You can end therapy when you want to
There are no formal contracts binding you to your therapist. These sessions are entirely up to you; you pay each time you go, there’s no payment in advance. Your therapist may mark down a future time to meet after each visit, but you can cancel at any point.
If you don’t feel you’re getting enough, or anything, out of therapy, you can look for a new therapist or stop going altogether. While many people find therapy helpful, it is not a guaranteed aid for everyone. Or, perhaps you feel you’ve gotten all you can from your sessions and are now ready to take the next step forward independently. That is the ultimate goal of therapy, so you should be proud to get to that point. How long a person should be in therapy depends on their mental illness and the depth of their issues, but the decision to stay is ultimately yours.