Oh my, what shall I do?

I've been with the same guy for almost 11 months, and he wrote me a sort of upsetting note today. We've been through literal Hell and back with each other. He was my best friend before we started dating, and he doesn't think that he deserves me. If anything, I'm the one that doesn't deserve him. We used to fight really bad, and we still have our moments, but we've fixed all the rough spots, and we're really good now.

It worries me that he feels that way, and I told him it was the dumbest thing that he could have ever told me. I love him so much, he is my life. Literally. If I wouldn't have met him, I can honestly say that I wouldn't have typed this up today, because I wouldn't be here to have done it. I think I fixed it, but I'm not sure. I can't lose him...