The analyses of a text #4

The narrator recalls his adolescence.
He took a long journey, after his young wife died of a disease.
He got a letter from his old friend Agnes.
Chapter 58 ABSENCE
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I read her letter many times. I wrote to her before I slept. I told her that I had been in sore need of her help; that without her I was not, and I never had been, what she thought me; but that she inspired me to be that, and I would try.
I did try. In three months more, a year would have passed since the beginning of my sorrow. I determined to make no resolutions until the expiration of those three months, but to try. I lived in that valley, and its neighbourhood, all the time.
The three months gone, I resolved to remain away from home for some time longer; to settle myself for the present in Switzerland, which was growing dear to me in the remembrance of that evening; to resume my pen; to work.
I resorted humbly whither Agnes had commended me; I sought out Nature, never sought in vain; and I admitted to my breast the human interest I had lately shrunk from. It was not long, before I had almost as many friends in the valley as in Yarmouth: and when I left it, before the winter set in, for Geneva, and came back in the spring, their cordial greetings had a homely sound to me, although they were not conveyed in English words.
[David Copperfield by Charles Dickens]
1. I'd like to know if "more" means "again."
2. I'd like to know "whither" means "the place on which."
3. And I'd like to know why it is "the human interest," not "humans."
Thank you in advance for your help.