postman to heaven

have you ever watch or read postman to heaven movie/ comic? whos jaejong be the main actor there^^
theres one letter that really make me sad and crying. that was from an old man who send a letter to heaven for him wife, it says:

"my wife
my wife, i never imagine that you will gone before me
after you gone i feel so lonely
how is your home now?
my wife...
actually i found something surprising when i clean up your stuff
a love letter, exactly
who is him?
who is that man? i dont know about him
it's full of passion
dear, are you..
give your heart for him too?
or, our son Geon Woo
Geon Woo is your son with him...
i can't sleep think about it"

i don't know why is him wife must cheating him, its really not make a sense to remember that she has a husband like him~