Complex sentence: While hiding from Tanner's posse, Valdez is informed by Gay Erin that it was she who killed her own husband in order to be with Tanner, not the other way around.
Split into simpler sentences: While hiding from Tanner's posse, Valdez realizes that Gay Erin knows who killed her husband. Valdez confronts her and she admits that it was she who killed her own husband in order to be with Tanner, not the other way around.