Forgiveness is only as hard as you make it.
You have to remember that everyone will make mistakes, some greater than others. Even you will make mistakes and hurt people. If someone asks you to forgive them, put yourself in their shoes. You would want to be forgiven, wouldn't you?
You can't change what has happened in the past, you can only learn from things and hope that the future will be better.
Don't dwell on things you can't change.