"He that covereth his sins shall not prosper; but whoso confesseth and forsake them shall have mercy"- Proverbs 28:13
In the offence of a person, friend, or neighbour, you must admit your wrong and it becomes their duty to forgive you.
You are then free to seek God's forgiveness.
Why? Because the individual wronged is a creation of God and in injuring him/her you have sinned against the Creator.
A sin against man is a sin against God!
[Taken from 'Steps to Christ']