Why do the Micawbers to go to Plymouth? How does David feel when he hears about the Micawbers leaving?

Now that Mr. Micawber is out of trouble, the Micawbers have no reason to stay in London. Plymouth presented new opportunities for Mr. Micawber, and Mrs. Micawber wasn't going to let him leave unless she went along. Their departure left David uncertain.... he didn't know where to turn. Their leaving left him feeling hopeless.

I had grown to be so accustomed to the Micawbers, and had been so intimate with them in their distresses, and was so utterly friendless without them, that the prospect of being thrown upon some new shift for a lodging, and going once more among unknown people, was like being that moment turned adrift into my present life, with such a knowledge of it ready made as experience had given me. All the sensitive feelings it wounded so cruelly, all the shame and misery it kept alive within my breast, became more poignant as I thought of this; and I determined that the life
was unendurable.