There is no civil war in hell

Our Lord is accused of being in league with devils by the pharisees when he casts out devils. Our Lord says "Every kingdom divided against itself, shall be brought to desolation, and house upon house shall fall Luke 11:17". Our Lord warns them; all sins will be forgiven, all blasphemies can be forgiven, but he who blasphemes against the Holy Spirit he will never have forgiveness, because he is guilty of a eternal sin. What is this eternal sin, the sin that cannot be forgiven?