Catrin,
It doesn't sound like an easy situation. I imagine it's very difficult to walk that delicate line with someone facing a serious illness between being postive/optimistic while not dismissing their very real and legitimate fears. I feel for the spot you're in.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher