In what way did sensei betray k?

Sensei's misanthropy develops from two incidents. The first is his uncle's cheating him of his inheritance; because he and his father had trusted his uncle so much, the betrayal was all the more painful. This shattering of innocence, which Sensei described as an inverse of the moment when an adolescent boy sees beauty in the world, especially in women, combined with a budding doubtful nature that Sensei already had, made him turn against the toward with great distrust and disdain. Nevertheless, he still retains confident in his own virtue, until he himself commits a terrible act of betrayal, which makes him hate the entire world, himself included.