The analyses of a text #3

The narrator recalls his adolescence.
He visited his old friend Traddles' place for the first time, and there met his old friend Mr. Micawber as Traddles' land lord who had been debtor quite a while.

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I am at present, my dear Copperfield, engaged in the sale of corn upon commission. It is not an avocation of a remunerative description - in other words, it does not pay - and some temporary embarrassments of a pecuniary nature have been the consequence. I am, however, delighted to add that I have now an immediate prospect of something turning up (I am not at liberty to say in what direction), which I trust will enable me to provide, permanently, both for myself and for your friend Traddles, in whom I have an unaffected interest. You may, perhaps, be prepared to hear that Mrs. Micawber is in a state of health which renders it not wholly improbable that an addition may be ultimately made to those pledges of affection which - in short, to the infantine group. Mrs. Micawber's family have been so good as to express their dissatisfaction at this state of things. I have merely to observe, that I am not aware that it is any business of theirs, and that I repel that exhibition of feeling with scorn, and with defiance!'
[David Copperfield by Charles Dickens]
1. I'd like to know why there is "which" is.
2. I'd like to know what "to those pledges of affection which" means.
3. And I'd like to know what "an addition is made to the infantine group" means
Thank you in advance for your help.