He was putting so much blame on her that he was going to lose her by holding the gun without pointing it at himself. He had abused their marriage vows for years, but he might not have a star to come home to if he kept pushing it. He just knew he would have a hard time controlling that dramatic mode once it set into play.
He wanted Theseus to pay because he couldn't brutalize Ariadne. "I do trust you..." but those words felt a little lopsided in his mouth as Eros had made sure to put a hole in their relationship.