Btukfyl

Writing to the woman who would become his third wife, Hermann Hesse complained: “Life for me now holds almost no pleasures any more, in fact I am living in Hell.” The event that had reduced Hesse to this state of near-despair was that his wife-to-be Ninon Dolbin had moved some of his books without his permission. For him this was an intolerable disruption of the orderly existence he believed essential to a writer who had detached himself from the world. His independence required that he hold all of humankind, and even his closest companion, at a rigorously policed distance . Accordingly, although the two of them lived under the same roof, he communicated with Ninon mainly in writing. As his latest biographer, Gunnar Decker, relates: .........

Can you paraphrase the highlighted part please? The reason I am asking is that what I do not understand when it comes to translating this passage is how it says once orderliness was essential to a self-isolated writer like Hesse and immediately it says his independence required he hold of all humankind . How if he is detached he needs to hold of humankind? Eventually he needs to be alone or connected?
And later when it says “ even his closest companion” why it says “even” ?

"Hold" does not necessarily mean keep close. It simply means to grasp in one's hands. Imagine picking up something dangerous -- you would not want it near your body, so we might say you would, "hold it at arm's length to keep it as far from you as possible.

In this case, of course, the use of "hold" is figurative. Hesse feels that a writer must, figuratively:

hold all people at a distance, even the ones closest to him.

"Even" is used to emphasize that Hesse's ethos applied to everyone. His dedication seems fairly extreme, given he feels like he is "living in Hell" just because his fiancee moved some books. But then that's probably part of the reason she was his third wife.

Anyway, you can use this definition, to "hold [some view]", in any number of ways:

He held her in high esteem, always praising her in public.

She held a low opinion of anyone else's opinions on the subject, dismissing their complaints out of hand.

At home, the mother held her family to the highest standards of cleanliness, and would not let the children leave the house, even for school, until their rooms were spotless.

Note also that various other verbs can also be used this way, such as "keep", "maintain", "take", and many others.

He took a low view of close personal relations, preferring to keep all of humanity at a distance.