The fear of trusting is called pistanthrophobia. Pistanthrophobia is considered a form of a social phobia and may be more correctly referred to as a social anxiety.
Phobias are an emotional or physical reaction to a feared object or situation. Pistanthrophobia can be categorized as a social phobia that relates to a fear of intimacy and trust. Social phobias usually begin in puberty and increase in prevalence with age, but people who suffer from anxiety about intimate relationships often base this fear on past negative experiences. Various methods of treatment are used and can be effective in treating most phobias or social anxieties, including cognitive behavioral therapy, systematic desensitization and medication.