Summon, it's shit. But hold on. Enjoy the little things you can, the jokes you make in adversity. Enjoy making him a cup of tea. Create the celebrations of him and of both of you.
One our neighbours who has multiple cancers was told he had two weeks in Feb. He's v old, but here he still is and we've celebrated his birthday with friends, etc etc.
And, this sounds callous but isn't, think what you want to use the remaining time for.
Do you want to be married before his time is up, to proclaim publicly you are each other's in law as well as in fact? You can do it very very fast.
Get him to make a will. If he doesn't, it is dreadful for his next if kin to sort out. ( won't be you unless you have legal standing). Draw yours up at the same time. You can always leave your possessions to him, if you predecease him, ie if there is a cure or you get run over by a bus, that way it's a joint act of love.
Do you want to go away somewhere special to you, together? If you have longer than expected, you have more time to build on.
The hospital will have counselling. Take it up. You will need people in RL, outside the immediate family.
Thinking of you. 