Hello,
With him, life was routine; without him, life was unbearable. - Chapter 12.
In this case, the author used semicolons because, altought there is not any conjunctive adverb or coordinating conjunction, there is a preposition, which in this case is "without", that is linking two closely connected main clauses. There are 2 clauses, independent syntactically, but very close semantically. The author is giving us two different perspectives; however, they both has a deep relationship: having or not having someone. Finally, it is worth clarifying that, prepositions are used to establish a relationship between 2 clauses, like in this situation, for example.