If there is something I am sure of it is that people will disappoint us. Some may even betray us. It happened to me several times. I experienced disappointments and betrayal from those I thought I knew very well. Because of this, ended up being bitter toward them, and even lost sleep because of it.
One day I realized that unknowingly, I had given these people the power to make me miserable. So that same day, I decided to remove their power over me. I chose to treat them the way I want them to treat me as Matthew 7:12 commands, "In everything, therefore, treat people the same way you want them to treat you, for this is the Law and the Prophets."
Then I also chose to forgive them, for God's sake and for my sake; for God's sake, because I want to please Him, and for my sake, so that I will not become bitter anymore. But though I would forgive, meaning I would not count their sins against them anymore, I would not forget. I've decided to use the experience to make me wiser and careful in the future. If ever this happens to you, do not give anyone the power to make you angry and miserable. Instead, use the situation to mature in Christ.