shun - To persistently avoid, ignore, or reject (someone or something) through antipathy or caution

When David tried to join in the conversation at the club, they ignored him, and he suspected that he was being shunned because he had a different religion than they did.
reticent - Describing someone who is inclined to keep their thoughts, feelings, or personal matters to themselves, not expressing them freely.

He was reticent about discussing his past, thinking that there were details that she might not react well too.