There are small trust issues like not remembering to give your friend their change after they gave you money for a drink. Or not trusting someone to not eat your piece of cake in the fridge.

Then there are the bigger ones. Do you trust her not to sleep with your boyfriend? Can you rely on so and so to not talk shit behind your back? Do you trust him not to steal your credit card and spend two hundred dollars? The basis for one's trust is on instinct at the begining of meeting someone. From there it gets built up or torn down over the duration of your relations.

I think that once you do not trust someone with the bigger issues there isn't much use in being friends anymore. It seems like once a persons trust is really low enough it cannot be raised again regardless of what the actuality of events.

I hope I am wrong.