Depends on what type of friend. If this was your very best friend, and you are sure you want the relationship to change because trust cannot be regained… have a conversation. Let them know you no longer trust them anymore and your friendship has changed. You can still be civil and acknowledge them as a person… but change the boundaries. Don’t let them into your secrets and intimate circle. On the other hand, if this friend was someone “new” who you thought you could trust, but have learned you were wrong about that, cut them out. Just back off without the conversation. Your behavior will dictate how close they are… and trust will never be broken again because you will control how much they know, how close they get, and how likely they are to have the power to lie, cheat, and deceive you… leave them with no information… they lost the privilege.