Explain the circumstances that lead to The Red Cross Knight abandoning Una.

Archimago disguised himself as Una and tried to lure the Red Cross Knight into defiling her virtue, but The Red Cross Knight refused. Later, Archimago made himself appear to The Red Cross Knight as Una being unfaithful with another man. This outraged The Red Cross Knight, and he left in anger. He was very apt to believe this deception because of what had occurred the night before