why is Brad so sad?

There lived once a man named Brad
All of the time he was sad
Whatever happened to make him that way
No one knew or wouldn’t say

So his friends all went up to him
His porch filled up to the brim
They asked him "why, oh Brad"
That you are always so sad"

Brad looked up and said
"you all know about my wife Mary,
And how sometimes she can be scary.
her will is just isnt unmade"

"Last year Ted, my dog fell sick.
He couldn’t even muster a lick
The vet tried all that he could
But Ted wouldn’t even touch his food"

"it was then decided to put him down
A choice between a shot or to drown
I couldn’t bear to see him go
That much coldness I cant show"

But what must be done has to be done
So my wife went and fetched the gun
I tried to escape from the act
Said the gun was rusty in fact

Delayed the act as much as I could
Threw the can of oil out for good
Days merged into weeks together
And Ted wasn’t getting better either

One day I come home and see
Grinning and cleaning the gun with glee
I tread that the moment has come
That my feelings have to get real numb

I asked her for the gun
But she said the act's done
She knew that I couldn’t do it
And that I was too proud to admit"

The guys were shocked
"oh fool you got a great wife
Why are you sad
You should be happy with your life"

"I was I was" Brad insisted
"Till six months ago when my doctor visited
He found a dangerous tumor up my knee
In a place where no one can quite see

He told it has to be cut out soon
Or it will turn my leg a prune
I am scared of knives and surgery
I swoon at the very imagery

I delayed this as long as I can
Whenever the doctor came over I ran
And hid in the local bar
Didn’t go home till he left in his car"

"So what has got you riled up now"
Asked the guys, tired somehow
"last month I came home late one night
Saw mary doing something by the kitchen light"

I walked up close to her from behind
The look on her face seemed determined
She was cleaning a knife she had in her hand
Grinning about something that she had planned

From that day my friends, my sleep is gone
From that day, deep fears have born
I sleep now with one eye open
Dreading like a chicken let live to fatten

Now you tell me shouldn’t I be sad
Am I wrong or am I mad
What would you do if your wife
Sat by the bedside with a knife