We do not forgive to release ourselves from a burden. We forgive a repentant offender for the sake of the relationship. If we say we forgive for ourselves we are being self-absorbed. We ought to care more about the offender being cleansed from their sin than our own personal feelings.
We forgive someone who is repentant so that he/she can be restored to fellowship with us and with God. To "just let it go" to make ourselves feel better lacks empathy and concern for the offender whose life might be ruined because they have not learned to confess to God for forgiveness and to us for a restoration of our relationship.
We are to follow God's example with us;
Hebrews 12:5-9
"6 because the Lord disciplines the one he loves, and he chastens everyone he accepts as his son.”
Revelation 3:19 "19 Those I love, I rebuke and discipline. Therefore be earnest and repent."
Proverbs 13:24
"He who spares his rod hates his son, But he who loves him disciplines him promptly."
Discipline is a big part of loving others. Without it those who walk disobediently fall deeper and deeper into sin, even to the point of destroying themselves.
Ezekiel 3:18-19
"When I say to a wicked person, ‘You will surely die,’ and you do not warn them or speak out to dissuade them from their evil ways in order to save their life, that wicked person will die for their sin, and I will hold you accountable for their blood. But if you do warn the wicked person and they do not turn from their wickedness or from their evil ways, they will die for their sin; but you will have saved yourself."
We are to care so much about our Christian brothers and sisters that we are willing to lose them over the truth. If they don't want the truth that will save their life then there is nothing more we can do. Becoming more friendly only solidifies their choice and makes them comfortable with it. Then we become helpers, enablers in their sin.
Ephesians 5:6-8 "…6 Let no one deceive you with empty words, for because of such things the wrath of God is coming on the sons of disobedience. 7 Therefore do not be partakers with them. 8 For you were once darkness, but now you are light in the Lord. Walk as children of light,…"