How Do You Cope with A Minor But Lifelong Injury?

I injured my knee a few months ago by running, but I continued to run on it.It didnt' get better, and it's been nine months. i saw a doctor two months ago, and he said it was just a tear in my meniscus, my knee cartilage, and that it would probably just heal itself. Despite the fact that I had done nothing for nine months and gained weight, I was still hopeful to get back to running. I realize now that this minor injury is going to last my entire life, and it means is that I can never exercise again. How do you deal with this?