I don't understand?

The mother cries,
Tears fall on the letter,
Will things ever get better?
She doesn't understand,
Why he took his life with his own two hands.

Little did she know he was always under stress.
Hated his life, hated the world, always a mess.
Then one day he decided he had enough,
He made it quick and easy nothing rough.

He cocked the shotgun, and opened wide,
He said sorry and he said goodbye,
To the ones he loved, and to the ones that loved him,
And with his last breath he said: "This is my last sin.."