[Warning: Second-Half of the chapter contains mature content]
He couldn't let anyone else know of this side of hers as no one would understand her the way he does.
Chance was indeed not upset with her as he could understand her perspective. She has very less people in her life who mattered to her and after knowing the person she hates the most intends to kill the one she is close to, then she would obviously do everything in her control to protect her loved one.
He too would have done the same thing if Samantha wishes to kill David or his other friends. Therefore, he was really not upset with her.
He anyway wished to keep his life as Grim Reaper and as Chance separate from each other. Bill was already on his side, so there was nothing for him to worry about.