The best way to defeat mental illness is therapy.
Therapy is a treatment. It’s there to help you help yourself. Much like a cast on a broken foot, once that cast comes off, it’s up to you to do the exercises to regain the strength of the foot. Therapy is the cast of an injured mind, it’s there to help stabilize and support, but it’s up to you to put in the work (exercise, eating right, etc.) You may still be suicidal, you may still be a nihilist, none of these are inherently bad, but depression can be treated and helped with many tools. Tools that you must implement outside of the therapist’s office. If you think your therapy is not good enough to help you, it’s better to change your therapist. But don’t skip your therapy sessions. It works miraculously.