I know what you mean. The best way to overcome this is to give meaning to your life. Pick up a hobby. Maybe playing instruments or sports or exercising. The better you get at it, the better you will feel and the more alive you will feel. Decide on your future goals. Biologist, teacher, chef, engineer, whatever you want, aim for it and work hard.
You don’t have to say goodbye because you don’t have to kill yourself. Instead of contemplating suicide, think about how you can get better, about how you can recover, about how you can live your life, and about how you can be happy.