This is surely a tough time for you all. Just keep taking things day by day, or if needed - hour by hour, or even minute by minute. Especially for your son - tell him all he has to do is get thru the minute that is in front of him. (Don't borrow trouble from tomorrow, for today has worries enough of its own. _ that applies to hours and minutes, too.)
For both you and your son, when things get tough, step back a moment, take a couple of big deep breaths, refocus, and then move on. No sense letting things overwhelm you, cause the only thing you can control is the moment you're in right now, and controlling that moment well will help to make the next moment better than the last.
Once you and he feel more in control - as you will, it will get easier to start looking at the larger picture.
I wish you well - hang in there. Lots of us have learned how to kick cancer in the butt, and you will too!
Sincerely, Tre