If God pardoned us on the cross, are the repented just self confirmed or is it a side effect of Gods will?
They are confirmed by God. Note that neither the sheep nor the goats, in Matthew 25, were aware that Jesus was among them. The sheep were separated because they received their inheritance. The goat were separated because of the curse that remained upon them.
When God makes someone alive in Christ by grace and gives the gift of faith, the person will repent.
God confirms the elect. God enables the elect to persevere precisely because He has given them faith.
Self confirmation is not necessarily accurate. The goats thought they were saved, but they were not.