If only I am his wife...

If only I am his wife...
I am a terminal-sick-boy sister.My younger brother suffered
from cancer and can't survive long.He is only 19 years old.
His only regret is that he has never tasted the fruit of love.
He doesn't want to pass his life with this regret.As his
sister,I really want to complete his hope by offering my
verginality to him and don't let him regret being born
in this world.Is it justable from the moral aspect?
I love him dearly.He is a cute and lovely boy.
I don't want him go with regret.I want to
help him fulfill his wish.