first ,i must know what he has done that betrayed me.if it not very important i will give him a change to make up.but if it very serious,i must have to don't give him any reasons.and i don't want him to be my friend again.
it depends on the situation. most of the time, forgive people who are like them.
We should always learn to forgive and give them another chance. but also, we should learn from our mistakes. twice is enough.