Sisters, But It's Okay

My husband almost slept with his sister. Soon after, his brother-in-law, who keeps coming to mind leaves after realizing that he does not love his wife. And the older sister's husband, Jeong-wook, visits the sister-in-law in anger, but the sister-in-law also suffers from not accepting this situation. The two who flirted like that commit another affair, and Jeong-wook soon feels guilty.