Love Junkie

Right after graduating high school, Yewon falls headfirst into an affair with the charming but married Han Ju-eon. She knows it’s wrong, but she doesn’t care. She’s in love. “I want to hear you say it. Are you having an affair with that guy?” “Fine! We're having an affair. So what?” Things start to spiral when their classmate Jeong Hwa-ik catches them in the act and makes her an offer of his own. Whether out of spite, curiosity, or something darker, she agrees. "Even if I sleep with someone else, you’re not going to leave your wife, are you?"(Source: Lezhin US) Note: Includes one extra chapter.