Matthew 6:14-15 says:
"For if you forgive other people when they sin against you, your heavenly Father will also forgive you. But if you do not forgive others their sins, your Father will not forgive your sins." - Matthew 6:14-15
It's often true that we have no problem accepting forgiveness from God for our sins but when someone sins against us, that's another story. Whenever we are sinned against, we must choose to remember the extent to which God has released us from our sins through the blood of His Son (Revelation 1:5). Our horizontal forgiveness of other sinners is related to our vertical forgiveness from God.
Remember, forgiveness is not a one-way street, it's meant to be shared with everyone.