Being betrayed
Consider the situation as learning experience for yourself. Distinguish between intentional and unintentional betrayal (assuming the latter exist). Realize how insecure the colleague, who betrayed you is. Let go of anger toward him for your own sake. Remain friendly on the surface and keep interactions professional. Choose to forgive but never forget. Try rebuilding trust instead of retaliating. Keep an eye on the other person’s behavior changes. Relate him accordingly.