The Devil sins against us when he leads us astray, but we are to forgive those who trespass against us; so should we forgive him? Does God?
It's true that we don't get to blame him for our own sins, but I'm thinking that he has done as much damage in God's creation as Adam and Eve. So it can be natural for us to hold things against him. Still, "When you stand to pray, forgive anyone against whom you have a grievance, so that your heavenly Father may in turn forgive you your transgressions" (Mark 11:25).