The analyses of a text #5

The narrator recalls his adolescence, now about her ill wife.

Chapter 53 ANOTHER RETROSPECT
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What a strange rest and pause in my life there seems to be - and in all life, within doors and without - when I sit in the quiet, shaded, orderly room, with the blue eyes of my child-wife turned towards me, and her little fingers twining round my hand! Many and many an hour I sit thus; but, of all those times, three times come the freshest on my mind.
It is morning; and Dora, made so trim by my aunt's hands, shows me how her pretty hair will curl upon the pillow yet, an how long and bright it is, and how she likes to have it loosely gathered in that net she wears.
'Not that I am vain of it, now, you mocking boy,' she says, when I smile; 'but because you used to say you thought it so beautiful; and because, when I first began to think about you, I used to peep in the glass, and wonder whether you would like very much to have a lock of it. Oh what a foolish fellow you were, Doady, when I gave you one!'
'That was on the day when you were painting the flowers I had given you, Dora, and when I told you how much in love I was.'
'Ah! but I didn't like to tell you,' says Dora, 'then, how I had cried over them, because I believed you really liked me! When I can run about again as I used to do, Doady, let us go and see those places where we were such a silly couple, shall we? And take some of the old walks? And not forget poor papa?'
[David Copperfield by Charles Dickens]
1. I'd like to know what "have a lock of it" means
2. I'd like to know what "one" refers to.
3. I think "them" refers to the clause in blue.
If so, I was wondering why it is "them," not "it."
Thank you in advance for your help.