Narcissus read what Echo wrote, before going back to his admiration of Echo's stomach and the child within it. "See?" He looked up at Echo again. "He likes us here together, the three of us. And I want to do everything I can to make him happy." This was equal parts manipulation and true feelings. He did want Echo back, and he did want his son to be happy, but he also had his own motives.
"This is why I want you to move back in. You're having a son with me, whether you like it or not, and he deserves a family, don't you think? I'm willing to bet that he doesn't move so much when Himeros speaks to him, and Himeros could never love him like I do." Narcissus looked up at Echo. "Besides, you know you still love me."