It is very difficult if you are disappointed. Sometimes you just simply want to get even. However, you want to obey God but again you are hurt. You want to explode, you want to kick the person, you want to disrespect, you want to punch him and many other things.
I guess a strong heart is not enough to absorb the pain because at the end. We must and should desire Christ likeness in our lives.
I found this article by Precepts for Life (Give Thanks In the Midst of Disappointment by Kay Arthur). A very good find and I hope that this will encourage you to trust God more in times of disappointment.