The analyses of a text #3

The narrator recalls his adolescence.
He is an apprentice of the proctor, Mr. Spenlow.
He visited Mr. Spenlow's place, and because he fell for his daughter at at first sight, he didn't hear nothing and noticed the presence of another woman when he was introduced to his daughter Dora and her confidential friend, Miss muderstion, the narrator's ill-tempered step-father's elder sister.
The next day morning, he is walking about Mr. Spenlow's garden, thinking about Dora when he meets Dora.

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In short, she was shaking the curls again, when the little dog came running along the walk to our relief.
He was mortally jealous of me, and persisted in barking at me. She took him up in her arms?oh my goodness!?and caressed him, but he persisted upon barking still.
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'You are not very intimate with Miss Murdstone, are you?' said Dora. -'My pet.'
(The two last words were to the dog. Oh, if they had only been to me!)
'No,' I replied. 'Not at all so.'
'She is a tiresome creature,' said Dora, pouting. 'I can't think what papa can have been about, when he chose such a vexatious thing to be my companion. Who wants a protector? I am sure I don't want a protector. Jip can protect me a great deal better than Miss Murdstone, - can't you, Jip, dear?'
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Jip made a comfortable noise, in answer, a little like a tea-kettle when it sings. As for me, every word was a new heap of fetters, riveted above the last.
'It is very hard, because we have not a kind Mama, that we are to have, instead, a sulky, gloomy old thing like Miss Murdstone, always following us about - isn't it, Jip? Never mind, Jip. We won't be confidential, and we'll make ourselves as happy as we can in spite of her, and we'll tease her, and not please her - won't we, Jip?'
If it had lasted any longer, I think I must have gone down on my knees on the gravel, with the probability before me of grazing them, and of being presently ejected from the premises besides. But, by good fortune the greenhouse was not far off, and these words brought us to it.
[David Copperfield by Charles Dickens]
1. I'd like to know what "what papa can have been about" means.
2. I'd like to know why it is "above," not "by."
3. And I'd like to know what "probability before me of grazing them" means.
Thank you in advance for your help.