In Ephesians 4, we are given some guidelines on being mature. They really aren't all that hard to abide by:
Be completely humble and gentle
Be patient bearing with one another in love
Keep the unity of the Spirit through the bond of peace
Put off all falsehood and speak truthfully to everyone
In your anger, do not sin
Do not let the son go down while you are still angry
Do not give the devil a foothold
Do not let any unwholesome talk come out of your mouths, but build others up according to their needs
Rid yourself of all bitterness, rage and anger, brawling and slander and every other form of malice
Be kind and compassionate to one another, forgiving each other, just as in Christ, God forgave you.
I can only guess Paul saved forgiveness for last, because we all will in some way mess up on the earlier ones and end up hurting someone.
Forgiveness is a strange thing. If someone bumps into you, and knocks something out of your hands, we will most always forgive them right away. It's when things start to hurt more that we find it harder to forgive or even forgive at all. The thing of it is though, the bible says forgive, just as we were forgiven...no levels of hurt, just forgive and be genuine in it. God knows your heart.
Yes, forgiveness can be very hard, but with Gods love in us, we can do it, He wants us to.