Hang there. The odds are that he's not suffering from cancer, and if he is... with our medical knowledge and technological advancements, the prognosis for the vast majority of cancer patients is really good. MY mom is currently (As in, literally right this moment) undergoing chemo. It's scary, it's tough, but it's SURVIVABLE. Cancer is NOT a death sentence. It's a bump in the road... nothing more.
You can do this, and you will. He needs you to be there for him, and don't let him chase you away. Some men have the same tendency as cats; they want to push away the ones they need the most.
Don't let him. ;)