It's heartbreaking when you know you're fighting a losing battle, wondering if every day is the last one. All I can say is make the most of every moment you have with her, make them into a lifetime rather than waste them worrying about the future. A quote from Tennyson's Ulysses used to give me strength and reminded me that it's only circumstances that have changed, the person is still the same, still the one you love.
Though much is taken, much abides; and though
We are not now that strength which in old days
Moved earth and heaven, that which we are, we are,
One equal temper of heroic hearts,
Made weak by time and fate, but strong in will
To strive, to seek, to find, and not to yield