Having someone, especially a friend, stab you in the back can be a difficult predicament. If the person who stabbed you in the back is a person you have to see on a regular basis, you may find that it becomes increasingly difficult to deal with him. Handling the situation in a mature manner will speak volumes about your character.
Be nice to the back stabber. Stooping to her level will make you seem immature. Remaining courteous will make it appear that you are unaffected by her actions. This may make her wonder why she stabbed you in the back.
Consider your words carefully. Keep in mind that anything you say to him, he may repeat to others, and sometimes out of context. If the back stabber is a person who works with you, it is especially important that you say only positive things around him.
Keep your distance from the back stabber. This may be difficult if you work with her or if you have a lot of mutual friends. If you have to be in the same vicinity as her, deal with her as little as possible. It is important that you refrain from getting into a situation where tempers may flare.
Talk it out calmly. Make sure you pick a time when you are calm and relaxed to talk to him. Your conversation should be private. You should do this if you want to try to maintain some sort of friendship with the back stabber. Take into consideration the fact that it may be hard for you to ever trust him again.