My wife has cancer

My wife of 11 years has cancer, she's been doing chemo for a couple of months now. We're in our early 30's with 3 kids and I just don't know why us? We're pretty good people, my wife is an excellent and caring person who had a horrible upbringing. I feel it's messed up she has to suffer when she's suffered so much in life already. I'm breaking down mentally watching her go downhill and idk how to stay strong