Simon hasn't been faithful to his wife for a lot of reasons, mainly because it was an arranged marriage and he didn't like her, he even dodged having kids with her because he didn't want to be stuck with her. But it was different with you, he knew his heart belonged with you, someone who made him feel raw emotions, love, desire and passion. He just didn't know how would he leave his wife. He wanted you to be his, he wanted to be faithful to you and no one else.