When Che realizes that Miranda is not actually in an open relationship, they retreat. While Che enjoys challenging tradition, one line they won't cross is being a home-wrecker. They tell Miranda that they cannot pursue a relationship with her any further unless Miranda figures out what she wants from life. As a result, Miranda finally tells Steve she wants a divorce. Poor Steve tells her that he feels like he's never been enough for her, but he's tired of hanging on and fighting for them.
Steve wonders if Miranda really knows what out there on the dating scene now. Miranda continues to salt Steve's wounds even further by fessing up that she's already met someone (we couldn't help but wonder, would she still divorce Steve if she hadn't met Che?). Che had confessed to Miranda earlier in Episode 8 that they loved her too, before leaving for a show in Cleveland. This was the main motivation Miranda needed to act.