Though Im so sorry to hear of people going through a similar thing, It is definitely comforting to hear of other people's experiences. I'm 26 and my mum was diagnosed with terminal Bone Marrow Cancer in 2015 (though she only told me and my brother in 2017, as I think she had a dream that she could get better and then tell us afterwards...!). I am so grateful that she is still with us and still fighting, though it is so hard to see her go through times when she is so ill. She is the person who I've always shared absolutely everything with, and the thought of her not being here is incomprehensible.
For me, It's the unknown future that is really tricky. We go through rollercoaster times when she is fairly well and progressing and geting stronger, able to drive still and get out of the house on her own, to quickly going downhill and deteriorating. She is back in hospital at the moment with shortness of breath due to heart failure and it feels like we are back to a very scary time again. I certainly feel uncomfortable thinking too far into the future and entirely agree it is more mangeable to take it day by day. Her attitude is unbelievably positive also, so that makes it somewhat easier (though makes me question further my kind of 'faith' in good things happening to good people etc). It's certainly made me question the bigger picture, and I'm yet to find something that explains it in a way I find comforting, but in the meantime it's lovely to connect with other people and be able to talk through it.
Best Wishes
May