I love how Jinwoo explained marriage and his love for Yujeong. I could totally relate coz I am married myself. As years go by, you become comfortable, sometimes, too much with each other that the romance is neglected. That does not mean that you are no longer in love with your partner. That scene really made me teary-eyed. Made me call my husband and say how much I love him.
I think, like most marriages, husband and wife get bored with each other (leads to infidelity most of the time). Despite the boredom, Jinwoo isn't cheating on Yeo Jung so that speaks alot about him. He also feels like he was emasculated by his wife but he didn't leave the marriage. I am not making excuses for his behavior because a lie is still a lie, at the end of the day. I just understand where he is coming from. Husbands still like their freedom but they also need a home/family/wife to go back to, because this is where they find their emotional security.