Dave brings up a really good point...forgiving someone does not mean that you are excusing their bad behavior...what it really means is that you are choosing an act of grace that allows both parties to heal and move forward in the relationship (if it is still intact) and in life.
In fact you don't even need to consider the forgiveness for the other person(s)...many times it is for your own benefit! One should not live with bitterness and resentment. Sometimes the people we need to forgive don't deserve it...or even want it, so it is in those times that the act is actually just for our own healing and progress.
Easier said than done though, right? Forgiveness may be one of the hardest things that we have to ever do. Maybe that is why there are so many books written on the subject! You many want to check these out:
All the best,
"Courage is not the abscence of fear, it is feeling afraid and doing it anyway!"
"Worrying does not empty tomorrow of its troubles...it empties today of its strength."
Corrie Ten Boom
Panic Syndrome recovery due to CBT