im assuming you dont mind spoilers so ill start from the start, they got engaged because of a contract and ido didnt have an interest in sejin at all. basically he was cold as hell to him and allat. after a while they started talking more but it didnt last long. sejin was forced by his father to steal files/documents and everything that happened in the manhwa as well, but in the past ido lost all of his trust for sejin and basically ignored him like he wasnt even in the house. if i remember right when sejin was in heat he needed someone and kept calling ido (this might be incorrect cause i read the novel mtl) and he didn’t answer. out of nowhere ido’s brother appeared searching for ido in his house but since ido hated being in the same house as sejin only sejin was there. he took the opportunity of him being in a vulnerable state and r@ped him. after a while ido finds out that his brother was home while sejin was in heat and thought he was cheating on him and out of rage he r@ped him as well. it was terrible. sejin got pregnant but didnt know who the father was so he became extremely depressed and starved himself. seeing how ido still didnt care about him and he didnt want to give birth not knowing who the father was he shot himself with the gun in ido’s office.
the info may not be 100% accurate since i read the novel translated by a mtl and i may have excluded some details cause i have the memory of a hamster
To me it's basically the relevant details that matter to understand the story.
Oh f*ck ! That's terible. I'm not surprised about the suicide coz i already saw the gun. But the r*pe thing ? I can't.
I'm itching to know what happened in the past . Tho , i have a bit of an idea.