Basically inseo told yihyeoks mom that he loves him and his mom was terefified because yikhyeok dad was basically abusing her and that's what she thought all men were like and she didn't want yikheok to go through all that but she had a crush on inseos mother so she didn't want to harm her family in any way and that made her suffer a lot(her mental heatlth) so in the end she decided to leave and fun fact yikheok mother is bi (or les) and inseo is scared that yikheyok will know the truth and then he would never love him again even though inseo truly loves him he's scared because he the root y his mother left. (The reason why I know this is bc the raws r at chap 51).