It's awesome. it's kind of a cross between Tuesdays With Maury and The Black Tulip by Alaxander Dumas. ~ only with chocolate. You can have a whole side plot describing how its made and all the care she puts into doing that, and how she works with him. The reader is wondering then, what's more important the chocolate or him?
You can have him move from the surprise, anger, depression acceptance phases of the disease and how it affects their relationship.
If you don't write this, I will.
Edit: Look people, It doesn't matter if it is a cure for cancer, suppose he starts feeling better and maybe there is something in her chocolate, There's a subplot in Black Tulip where the neighbor is trying to steal the one of a kind tulip, do the same thing there. Everyoen pointing out that chocolate doesn't cure cancer is making the story more enticing: Does it? Did it and I didn't know? is there soemthign special she's doing? An ingredient? Is it love? Does he think he;s getting better and he's really not? Is he going to die?
You're all sucked in and don't realize it.