One of my favorite quotes to help keep peace in your mind and heart comes from Buddha, who said “holding onto anger is like drinking poison and expecting the other person to die.”
Forgiveness truly is the gift you give yourself. Most of the time when we stay angry at people it only affects us. Think of what happens to your body when you get angry. Your blood pressure rises, you can get sick to the stomach among many other unpleasant symptoms. Imagine what would happen if we did this over a prolonged period of time. Not only would it drain our spirit and soul, but it would make us actually physically sick.
Here is the caveat about forgiving someone, it does not mean they need to be your best friend. There are some people who are destructive and surrounding yourself with them will only bring you down. I compare it to continuing to try and pet a dog you know will bite you. Unless the dog goes through some training, it will likely bite you again. Forgive the dog for biting you and then do your best to keep your distance from the dog.
Starting today, let go of anger and practice forgiveness. It does not mean you agree with their behaviour. It also does not mean you have to let them back into your life. It only means you value yourself enough to let go of negative emotions that will bring you down emotionally, spiritually and physically.