By the time Megan Grehl finally met Côme Ménage, it felt as if their relationship was meant to be. Both had studied architecture and urban design internationally, and when Ms. Grehl landed in Shanghai in 2009 to work at the design firm Neri&Hu, she heard stories about Mr. Ménage, who had just left. “We missed each other by a month,” said Ms. Grehl, 37, who now runs her own interior design studio. “Our friends were like, ‘Oh, it’s too bad. You just missed Côme. He went to New York, and you guys would have gotten along so well.’” Ms. Grehl…