The speaker admits a fear of making friends, and then explains it with a blunt, slightly comic image: a hog loose in a small home garden, crashing over a rose the speaker thought was wonderful. The speaker seems to see themselves as the hog, big and clumsy, while a friend is the delicate rose. Closeness, in this picture, risks damaging the very thing that was valued.
The title, "Self-neglect," suggests the speaker avoids people as a kind of protection, though it may also mean the speaker thinks poorly of themselves and so keeps away. The "little home field" gives a sense of a small, fragile space where there isn't room for a mistake.
The mood is wary and rueful. There is shame in the comparison, but also tenderness, since the speaker clearly cares about the rose. The loneliness here comes from caring too much about doing harm, not from indifference.