Dear Mr,X,
You've been in China for there years and now you're leaving to somewhere else.I just want you to be happy and always lead a good life wherever you are.I wonder whether you've fell in love with my country and its people,maybe three years is not long enough,someday in the future you should come back and enjoy it again.I just make a wish that everything could be more gorgeous for you,such as condition of work and love of families.
Warm regards.
XXX