Mark believes that most of his so-called friends actually are conspiring against him and would betray him if given the opportunity. as such, he is emotionally guarded and does not reveal personal secrets to anyone. mark's behavior is consistent with which personality disorder?

Based on the description, Mark's behavior is consistent with: Paranoid personality disorder.
People who have paranoid personality disorder tend to be in constant fear because they keep imagining a lot of unlikely scenarios that will cause them harm even though that scenario is far from the truth.