Forgiveness is a hard thing for us as a human being ,but if you have the mind of God, it will be easy for you to forgive your friend when he or she offend you.

And as a Christian God commanded us that we should forgive one another, even in our lord prayer,when he teach is discipline how to pray.

He said we should be pray like this our father who at in heaven, hallowed be thy name , thy kingdom come, there will be done on earth as it in heaven, give us these days our daily bread and forgive us our trespasses, as we forgive those who trespass against us.

And and for someone to receive forgiveness from god you must forgive others.

and concerning the question that you ask that how many time should we forgive anyone that offend us.

The Bible says 70*7 time in a day, which means seventy multiple by seven in a day and tell me can someone offend up to that number.

And someone who offend you today met be your best friend ever on earth or your helper tomorrow.

That is why we need to forgive ourselves, because even though when we do pray for God forgiveness, we say God should forgive the sin we know and the one we don't know.