Technically yes he did but he also didn't. At the time Honam was nowhere to be seen and Sooyeon was informed Honam was being wedding to the girl. It was safe to say they were over so he slept with his boss. But yes in reality Honam wasn't marrying her it was for show and Honam stupidy tried coming back. Honam did it to himself. He chose to forget Sooyeon rather than being with Sooyeon, he chose to go away for 4 months or whatever with no word to Sooyeon at all. What did he expect? This isn't like a military relationship. Even military people cal their spouses and the spoused call them. The spouses cheat out of being dickheads and impatient. Sooyeon was informed Honam was GONE. To him, he was single.