Firestar and Sandstorm’s relationship is a little more… complicated. Firestar doesn’t want her getting hurt for his choices, but she still wants to stay by his side. She will come to suffer for this.
Cinderpelt and Firestar have a strained friendship and bond. Cinderpelt understands where he’s coming from, she really does. She cannot agree with him. Firestar doesn’t blame her, for being unhappy with him. He could never.
Quickly after the TigerClan and BloodClan ordeal, Firestar tries to get Leopardstar to forfeit her lives to the moonstone and stand trial for her actions. She refuses. Firestar leads a coup, and kills her, so that Mistyfoot can receive all nine lives. He does NOT want a repeat of the Nightstar situation. Mistyfoot… doesn’t put up much of a fight to them killing her leader. Not after the treatment she and her brother had faced under TigerClan. After what Leopardstar let happen to them. This is the action that leads to Firestar becoming more extreme and violent.