Simon the Pharisee had an interest in Jesus, but he was not a believer. He wanted to see what all the talk was about. He may have acknowledged that Jesus was a teacher, but did not believe him to be a prophet, and certainly did not believe he was the Son of God. The woman believed much different. She sought Jesus for salvation. In this, the Pharisee still only saw a sinner. He did not acknowledge her repentance. We should be joyful when someone repents and gives their life to Jesus, and not judge them by their sinful past.
The moneylender forgave both of his debtors, as Jesus forgives all of our sins. Simon did not think he needed much forgiveness- he did not accept that he was a sinner. By thinking he needed no forgiveness, He loved Jesus little. He did not humble himself before Jesus as the woman did. The woman in contrast, humbled herself before Christ, anointed him as her king and savior, and loved him much. Our sin a a debt we cannot pay. Jesus paid it for us, all of our debt, for all sin. We are forgiven much, so we love much.