Like JPT, I would marry if I loved the person so much I would want to be with them until the end.
I actually knew a similar situation. The male cousin of my ex had a rare type of incurable bone cancer. The guy was good looking and had a winning personality. Once his girlfriend knew it was a terminal cancer, she left him. Maybe she just couldnt handle it and it was too painful for her. I would have stuck with him, but thats me and I cant blame her.
The only true wisdom is in knowing you know nothing.