You tell him that no matter what you become, you will stay with him and let him cheer for you.
But only if you love him enough. You'd better ask yourself before you say these things. If one day he really falls down, will you stay with him and never leave him? If your heart is still hesitating, don't say this to him easily, because once you make a promise to others, and you don't realize it in the end, it will be a great blow to him.
Let your love be his spiritual pillar. I wish him a speedy recovery. . . . . . .