1. putting loyalty in someone, and them turning theirs on you.
2. friends stabbing you in the back.
3. the most hurtful thing anyone can do.

Betrayal is when your fucking girlfriend decides to make up with/engage in sexual acts with another guy after all the great things you've given, offered, bought, done to her, with the excuse of "wanting to get more experience", thus leaving you with a broken spirit and with a bunch of emotions of hatred, loss of self-respect, loss of self-confidence, loneliness and total fucking sadness.

1. to turn on someone you trust, or to have someone do the same to you.
2. team-killing, i.e. in a FPS. More specifically, this is the term used when one team-kills in Halo/Halo 2.

when somebody does you wrong and back stabs you

You were booted from the game for betraying a teammate.

When your best friend deserts you for mean reasons and acts like a meany head.

The second book in The House of Night series written by mother-daughter-duo P.C. and Kristen Cast.