These people have obviously betrayed your trust which hurt you deeply. I think it's absolutely normal to think about hurting those who have hurt you as well because it is a way trying to find closure.

What Gayle says is right though. Please try to avoid these people as they will only bring you more trouble. It sounds to me like they will eventually mess up their own lives anyway.
You sound like a very loyal person and moral person; don't let a few jerks change you.