I know it may very much feel that way but to bring a bit of science into it; it's highly unlikely that you would be depressed for the rest of you life.
Instead what you're showing is "all or nothing thinking" which is a symptom of your depression, but certainly not an affirmation.
Well done on trying for help. But there's help in many forms, like for instance CBT, medication, mindfulness, hypnotherapy, cardio exercise, strength exercises, a period of travel, a helpful CD or book.
It may be one of them, it may be a combination of them, it may be something not listed there but there will be a day when you feel much better than you do now and probably sooner than you think.
Think of that day and aspire for it, then make a list and go and strive for it. When you do have a voice telling you you'll never find it then identify it as your disease.
A disease however that can and will be beaten. Never stop believing that even if your mind tells you other.