He mentioned that Van Gogh was not very strong, and so this was a very melancholy circumstance.
In several letters over the remainder of the year, Bonger comments on a growing appreciation for and friendship with Theo.Vincent van Gogh arrived in Paris in 1886 which meant that Bonger saw less of Theo.
Bonger expressed his concern that Vincent van Gogh was harsh with his brother Theo, who had begun to look haggard.
Theo met Bonger's parents during a visit to the Netherlands about August, 1886.Bonger went into the insurance business later in Amsterdam.
He was an intimate friend of Bertrand-Jean Redon, better known as artist Odilon Redon, and owned a large collection of his works.