I know the feeling. In my experience it goes away when the
depression goes away, and is therefore a symptom rather than a result of there actually being no reason to live. Unfortunately severe depression does not just go away overnight. Since it's severe enough that you're suicidal, you should probably be started on an anti-depressant. They take a few weeks to work though, and the first one may not work for you (there are many, and many combinations of them).