See, when you don't forgive, or if you don't fully forgive, what really happens, is you hurt yourself.
I know that sounds weird, but hear me out.
When someone hurts you, no matter how big or small... it could be that a neighbor ruined one of your plants while cutting the grass, someone ate your lunch out of the fridge, you were abused as a child, or you were cheated on by someone you trusted... forgiveness is necessary for YOU to move forward.
When forgiveness hasn't happened, or maybe it has in some areas, but not fully, guess what can set in? Bitterness.
Bitterness is a dangerous thing. It robs you of so much joy.
Forgiveness is not saying that what happened to you is ok.
Forgiveness is not saying that you have to be best friends with the person who wronged you.
Sure, you will worry about the future. (Even though you shouldn't.) I can hear you now, "But what if he or she does that to me again?" or "What happened to me cut to the core of who I am and made me feel worthless, how do I move past that and not hate this person for what they did to me?"
Colossians 3:13 says this, "13 Bear with each other and forgive one another if any of you has a grievance against someone. Forgive as the Lord forgave you."
Listen, God loves you. He does not want you to live in a prison of fear or unforgiveness. Let Him deal with that person. You know what you can do? Pray for the person who hurt you. God can fight for you, so you don't have to hold on to anything any more. Romans 12: 19 says, "19 Do not take revenge, my dear friends, but leave room for God’s wrath, for it is written: “It is mine to avenge; I will repay,” says the Lord."
It's a new year! Move into all that God has planned for your life and let this stuff go. You will be glad you did!