Quoting The Master:" Say your partner really really wanted a big family, and for recently diagnosed health reasons you're ... [snip!] ... and still love you, you know that they're miserable and deserve better. Would you let them go or be selfish and hold on?"
depends on what they wanted. True love... deals with hurdles life throws at us... through better or worse. but.. I also don't believe in being miserable. If he loved me enough to overcome that loss.. I'd hold on. I'd have to believe if he wants to be with me.. the loss of ME would hurt more than the loss of the life he expected.
but.. if the loss of the life he wished to have was more important than I was... then I'd let him go