Am I understanding correctly from your signature that your fiance still has ahead of him some kind of induction chemo and then the 7 weeks of rad/chemo combined that we all get? If so, they may be giving the grimmest part of the picture just to be clear about why all that is needed. It's not going to be easy, and, speaking for myself, I found the motivation to get through it from realizing what a nasty disease this is, and that I really wanted to fight it as hard as I could with all the weapons available.
It's almost like you have to become aware of the real risks of recurrence and death to give yourself the motivation to get through the fight. And then you at least know, if it does recur, that you did everything you could to fight it.
You're certainly at a great place for treatment, as Tim suggested, focus on getting through the treatment and recovery after. Beyond that, there's a certain amount that is beyond your control and that you have to just let go.
Nelie