Let's look at that passage from Matthew 6:9-15 NKJVI'll take one verse, Matt to forgive as the Father forgives.
God only forgives those who repent.
Which is what the Bible teaches. Yes we must forgive, we have to be able, ready, wiling o forgive but if the conditions are not met we don't.
Repentance is an attitude or an expression of sorrow or regret for something one has said or done.
9 In this manner, therefore, pray:
Our Father in heaven,
Hallowed be Your name.
10 Your kingdom come.
Your will be done
On earth as it is in heaven.
11 Give us this day our daily bread.
12 And forgive us our debts,
As we forgive our debtors.
13 And do not lead us into temptation,
But deliver us from the evil one.
For Yours is the kingdom and the power and the glory forever. Amen.
14 “For if you forgive men their trespasses, your heavenly Father will also forgive you. 15 But if you do not forgive men their trespasses, neither will your Father forgive your trespasses."
Also, in Luke 11:4 the Lord's Prayer uses this verse.
And forgive us our sins,
For we also forgive everyone who is indebted to us.
Also, in John 8:1-12, when Jesus forgives the woman He forgave her without she first repenting and then instructed her to "sin no more." We never do find out if she actually repented after this confrontation.
Somehow these passages must be reconciled with the Scripture you have pointed to unless we are to believe that God contradicts Himself.