Matthew 6:14, 15 "For if you forgive men their trespasses, your heavenly Father will also forgive you. But if you do not forgive men their trespasses, neither will your Father forgive your trespasses.
That is a scary verse - if I hold a grudge, and am unwilling to forgive someone for years or for one day ... God is unwilling to forgive me as well.
I read one time that when we are forgiven, God forgets it. In Philippians 3:13, Paul said "but one thing I do, forgetting those things which are behind and reaching forward to those things which are ahead." We have so much to look forward to, and to press onward towards ... it would be (dare I say silly?) unwise to let forgiveness towards others trip us up.