The analyses of a long text #3

The narrator recalls his adolescence.
His grand aunt and her distant relative Mr. Dick came to London after her going bankrupt.
He works as the secretary for Doctor Strong in his spare time, who was the head master of the school the protagonist went to.
One day, His best friend Agnes and her father, a local lawyer, Mr. Wickfield visited Doctor Strong.
And the next day, Mr. Wickfield's partner Uriah, who was once the clerk for him, came too.
One night, the narrator finds Doctor Strong, Mr. Wikckfield, and Uriah is together in a room.
Mr. Wickfield and Uriah have had a strong doubt that Dr. Strong's young attractive wife has a love affair with her cousin Mr. Maldon, and Uriah insinuated it to the narrator a few days ago.

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'My dear Strong,' said Mr. Wickfield in a tremulous voice, 'my good friend, I needn't tell you that it has been my vice to look for some one master motive in everybody, and to try all actions by one narrow test. I may have fallen into such doubts as I have had, through this mistake.'
'You have had doubts, Wickfield,' said the Doctor, without lifting up his head. 'You have had doubts.'
'Speak up, fellow-partner,' urged Uriah.
'I had, at one time, certainly,' said Mr. Wickfield. 'I - God forgive me - I thought YOU had.'
'No, no, no!' returned the Doctor, in a tone of most pathetic grief. 'I thought, at one time,' said Mr. Wickfield, 'that you wished to send Maldon abroad to effect a desirable separation.'
'No, no, no!' returned the Doctor. 'To give Annie pleasure, by making some provision for the companion of her childhood. Nothing else.'
'So I found,' said Mr. Wickfield. 'I couldn't doubt it, when you told me so. But I thought - I implore you to remember the narrow construction which has been my besetting sin - that, in a case where there was so much disparity in point of years -'
'That's the way to put it, you see, Master Copperfield!' observed Uriah, with fawning and offensive pity.
'- a lady of such youth, and such attractions, however real her respect for you, might have been influenced in marrying, by worldly considerations only. I make no allowance for innumerable feelings and circumstances that may have all tended to good. For Heaven's sake remember that!'
'How kind he puts it!' said Uriah, shaking his head.
'Always observing her from one point of view,' said Mr. Wickfield; 'but by all that is dear to you, my old friend, I entreat you to consider what it was; I am forced to confess now, having no escape -'
'No! There's no way out of it, Mr. Wickfield, sir,' observed Uriah, 'when it's got to this.'
'- that I did,' said Mr. Wickfield, glancing helplessly and distractedly at his partner, 'that I did doubt her, and think her wanting in her duty to you; and that I did sometimes, if I must say all, feel averse to Agnes being in such a familiar relation towards her, as to see what I saw, or in my diseased theory fancied that I saw. I never mentioned this to anyone. I never meant it to be known to anyone. And though it is terrible to you to hear,' said Mr. Wickfield, quite subdued, 'if you knew how terrible it is for me to tell, you would feel compassion for me!'
[David Copperfield by Charles Dickens]
1. I'd like to know why it is "by one narrow test," not "for one narrow test."
2. I'd like to know "were" is implied after "her respect for you."
3. I'd like to know the three blue "that" clauses are the objects of "confess."
4. I'd like to know what 'as to see what I saw" means.
5. And I'd like to know if what is the object of "saw" in blue.
Thank you in advance for your help.