Z,

I can relate to your experience in feeling betrayed, angry, hurt, and resentful.  I can relate on trying to figure out how to let that go.

What have you done to try to change how you feel?

Have you journaled about your feelings? Have you written an angry letter to your former friend (and not send it)?  Have you really allowed to be totally into your anger, ex. scream, punch a pillow (or other objects), swear, etc.?  Have you meditate on your anger where you just sat with those angry feelings and not try to make them go away?  Have you tried to re-write the story of your betrayal so you come out as a hero?

If not then try one or more of those exercises.

By the way, it is never wrong to feel whatever you are feeling or thinking.

Mark