Lack of trust is an enormous issue. If you don’t trust one person, it can filter through your entire life, destroying other relationships.
For today’s prompt, think of ways a person can destroy your character’s trust. Is it a best friend that betrays a confidence? An acquaintance that says or does something that affects your main character. Explore the facets of that broken trust. How does your character react? Do they stay in the situation and try to silently cope (yeah, that was me)? Do they lash out at everyone? Do they stop trusting others for no reason? If you want to go further, what steps would they need to take to rebuild trust. Could/would they try to rebuild a relationship with the person that they no longer trust? Why? Why not?