Putting myself in someone's shoes

Whenever I encounter difficult people, I try to understand why they're that way.  I imagine their lives and what shaped them into the person they are. 
Last week, yesterday, and today, I've had intense arguments with my father.  They're one sided, with him always right, and me just wanting peace.   I can't leave.  I've finally reached the conclusion that he is not acting normally.  He forgets conversations.  He's hostile.  He doesn't sleep.  And he's made my life a living hell. 
I'll be honest with you.  There's been times when I've entertained the fantasy that it was my husband who lived.  That's hard to admitt.  But I'm tired of being miserable. 
That's how I felt earlier today, when I got home from work with a brand new puppy for him, only to be greeted in anger that left me gasping for air.  Then I asked myself: if a man had lost a limb, would I expect him to be normal?  Would I expect him to get up without aide of a prosthesis and walk across the floor?  The answer is no because my knowledge of this type of injury keeps me from beliving that this man could walkl without help. 
And yet, I expect my father to be normal.  I expect it and I've lied to myself because of that expectation.
The fact is, he is sick.  Yes, he's always been a difficult man.  Yes, I've always suspected he had a mental problem, but now, it's worse.  He's forgetting conversations.  He's not able to follow simple instructions and he's desperately in denial.
So here we sit--two people with a pink elephant in the middle of the room, each hoping that somehow the thing would just disappear.  And it wont unless God wants it to because it is just to big.
Now, I'm left with a situation.  I can choose to run and hide, or I can put my pride to the side and just let things go as they may.  I must connnect to my own intellect and realize that I can't fix this and no amount of crying about my sad life is going to change this.  My father is not capable of being anything except who he is.  This condition has exagerated the person he has always been and I can't say I've ever liked that person.
Part of me is angry.  I'm here dealing with a potential disease.  I love him and want him to be normal.   I can't have what I want and my husband is dead.
There, I've said it.  My husband is dead.  I'm not using my usual words: passed, transition, etc.  He is dead to this current world.   And my father is alive and I love him.  If I didn't I wouldn't be sitting at my computer at 3:30 in the morning hoping to have things my way.  I've got to accept, things will never be the same.  And no amount of arguing with my father is going to change that.  And no amount of arguing with my father is going to make him see things my way.