Perhaps no action in life stings more than betrayal. To feel betrayed, you have to trust someone enough to be hurt by their unexpected actions. Recovering from this hurt can leave you unwilling to trust anyone in the same way for a long time. The psychological effects of betrayal are broad, even affecting the stability of societies. Trust is a basis for human existence, influenced by certain chemicals in the brain, such as oxytocin, a body chemical that accelerates trustful feelings. When going through your own betrayal, you can experience many related emotions.
The initial feeling most people experience when encountering a betrayal is shock. You're likely to spend weeks, months or even years in disbelief that the person who offended you was capable of her actions. Often times, trust is built over time and, based on witnessed behaviours, it takes time to reprogram your brain about the nature of this person's character.
After it settles in that your friend is capable of such a derogatory action, you are likely to experience some level of anger. It's common to get mad about letting yourself trust a person who was so insensitive and be furious at the betrayer. You may even have vengeful feelings of wanting to get back at that person, or hurt him in the same way he hurt you.
After the more caustic feelings of shock and anger dissipate, you may experience classic feelings of grief. If the betrayal is so great that you lose your relationship entirely, you may grieve that loss. You may also grieve what you thought you had with this person, which can be more difficult than letting go of something that actually existed.
If feelings of betrayal encroach greatly upon your sense of well-being, you may want to isolate yourself from others. Going out with your friends or making new ones seem less and less appealing. If feelings of isolation are allowed to go on for too long, you can even develop a social phobia.
Feelings of sadness are common after experiencing a betrayal. It hurts to have your trust in a person annihilated, and it's a logical progression of emotions to feel sad along the way. For those who don't work out their feelings and allow them to fester, they may even slip into a more precarious state of depression.