What does the Bible say about holding grudges and staying angry towards a person who did you wrong?
Here are some passages to consider:
For if you forgive men when they sin against you, your heavenly Father will also forgive you. But if you do not forgive men their sins, your Father will not forgive your sins. Matthew 6:14-15 (NIV)
Then Peter came to Jesus and asked, "Lord, how many times shall I forgive my brother when he sins against me? Up to seven times?" Jesus answered, "I tell you, not seven times, but seventy-seven times. "Therefore, the kingdom of heaven is like a king who wanted to settle accounts with his servants. As he began the settlement, a man who owed him ten thousand talents was brought to him. Since he was not able to pay, the master ordered that he and his wife and his children and all that he had be sold to repay the debt. "The servant fell on his knees before him. 'Be patient with me,' he begged, 'and I will pay back everything.' The servant's master took pity on him, canceled the debt and let him go. "But when that servant went out, he found one of his fellow servants who owed him a hundred denarii. He grabbed him and began to choke him. 'Pay back what you owe me!' he demanded. "His fellow servant fell to his knees and begged him, 'Be patient with me, and I will pay you back.' "But he refused. Instead, he went off and had the man thrown into prison until he could pay the debt. When the other servants saw what had happened, they were greatly distressed and went and told their master everything that had happened. "Then the master called the servant in. 'You wicked servant,' he said, 'I canceled all that debt of yours because you begged me to. Shouldn't you have had mercy on your fellow servant just as I had on you?' In anger his master turned him over to the jailers to be tortured, until he should pay back all he owed. "This is how my heavenly Father will treat each of you unless you forgive your brother from your heart." Matthew 18:21-35 (NIV)
And when you stand praying, if you hold anything against anyone, forgive him, so that your Father in heaven may forgive you your sins. Mark 11:25 (NIV)
Bear with each other and forgive whatever grievances you may have against one another. Forgive as the Lord forgave you. Colossians 3:13 (NIV)
I think it's important to remember a couple things about forgiveness. First of all, we serve the One who, while hanging on a cross, looked up to heaven and said, "Father, forgive them. They don't know what they're doing." (Luke 23:34) It is now He who lives within our hearts through His Holy Spirit and He can just as easily enable us to do the same.
Secondly, forgiveness does not necessarily mean that we have to let someone back into our lives. I think a lot of people wrongly assume that if they forgive someone they have to also throw open the door of relationship and open themselves to all the craziness and hurt. Not true. If someone has hurt you, it's in your best interest to forgive them, but it's possible to forgive someone and distance yourself from them at the same time.
If someone brings pain and craziness into my life, I'm going to be careful to forgive them (release them) but if they haven't changed their heart and behavior I'm going to take steps to make sure the same things don't just keep happening over and over again. If you have specific questions about your own situation I would encourage you to talk to your pastor.