Have you ever been blindsided in one day by a person who you trusted completely? What did you do about it?

This is a BIG question. When you put so much trust into a person because they seemed to be on your side and wouldn't do anything to hurt you and then they suddenly became this totally different person in one day that wasn't at all the person that you came to know.
How do people live with themselves after hurting another person so bad? Especially when the other person didn't do anything at all for this to happen.
Big betrayal that wasn't cheating or that has anything to do with sex.
Have you ever been blindsided in one day by a person who you trusted completely? What did you do about it?
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