When someone believes in you, and you doubt their worthiness, this hurts.. this hurts them like nothing hurted them like this. This breaks them inside. They start thinking that They are the only who is wrong.
If ever any of your friend starts distancing theirself from you, talk to them. Most important Believe in them. Trust that they are good humans just like you are. Spend time with them and know about them. They may hide something from you but don’t lose trust. Please believe in them. They may surely open their heart before you.
But if you start doubting them, Then again it will put them where they were or may be the more worse of the place where they were.
The Peace 