
basically, Jitae and Mi-Eum knew each other from the past. Mi-Eum’s dad kidnapped Jitae and was ordered to kill him due to being in debt and he would’ve got the money for it. Mi-Eum doesn’t remember anything but he been getting his memories back and now Hajoon told him everything. That’s how the S1 Ended

i missed some things too but basically mieum and jitae were friends from school and since they were really close to each other, someone(i think the step mom) made an offer to mieum's dad to kill jitae bc it was gonna be easier to catch him in the trap alone. so he did and seclude him in their home but mieum find out about it somehow and while trying to save him and take the bullet for him he became the one who got hurt and it caused his amnesia. the name tag mieum bring with him actually belongs to the blonde guy bc they were swapping clothes for jitae to meet mieum freely without getting caught. also according to the chapter before season finale, blondie backdoored jitae in the past too bc he said something like 'i'd do anything to see jitae crumble up' so i think he's an imposter too. this is what i understand so far hope this helps
someone explain please