
The one who r@ped Sejin was Ido's brother not Minjae. Sejin misunderstood and thought that Ido sent his brother to assault him, believing the 'gift' was from Ido, but it was actually a file containing his brother's crimes against other omegas. Ido also did, in fact, assault Sejin after feeling betrayed and also r@ped him because Sejin claimed to have willingly slept with his brother.

The part where seme regretted it is when they actually bonded after the seme raped uke (he thought that uke willingly slept with his stepbrother so he felt betrayed and raped uke after that) (based on cicadasatnight's reply)
so apparently in this story, bonded pairs could see the memories of their partner so after that bonding, seme could see through everything of uke's life and he regretted it alot. He avoided uke because of the guilt feeling (iirc he was doing something for uke too during that time, but i don't remember, probably handling uke's family issues at that time?)
So the regret grows to suicidal bcs he witnessed uke killed himself, right infront of him in that office(?) room and to find out that he was pregnant with their child too when uke killed himself.. he didn't get to make amends with uke
Seme regretted alot, like about how he didn't know that uke went through alot of abuse from his family and then seme were also abusing him (he treated uke very badly bcs he thought that uke was sent to marry him to sabotage seme's business)
So seme got suicidal with all of the guilt and killed himself
When he regressed, he did everything he could to protect uke from his abusive family

Don’t trust them! Trust me! Lol. I’ve read the novel. The MC was raped by Ido’s brother it happened during the chairman’s burial so nobody’s at the mansion. Ido’s brother went there bec Ido said he have a gift gor him. This is the time Ido started neglecting MC nobody in the mansion was allowed to talk w/ MC. It was a coincidence at that time MC was also in heat, so the rape happened. MC called up secretary Kim and want to leave Ido’s Mansion. Fast forward 3 days later Ido went to MC’s house not the main house, but MC’s own house. Ido already knows MC was raped and wants to take him back to the Mansion. That’s when MC proposed a divorce! That’s right they were married in their past life—not engaged. Ido was triggered and didn’t want a divorce so at the heat of the moment he also raped him and marked him.

Ido said to his brother, "I have a gift (file) for you at my house."
Sejin is at home and is in heat.
Ido's brother thinks that Sejin is the gift, so he rapes him and knots him.
Sejin thought that Ido gifted him to his brother.
Sejin moved out with the help of Mr. Kim and stayed at his officetel.
Ido finds Sejin there, seeing all the bruises on his body and intoxicated from the sleeping pills. (Sejin wanted to sleep to numb his pain TT.)
Sejin said that he slept with his brother willingly (which is not true) and asked for divorce.
Ido got mad, raped him, knotted him, and marked him.
Ido sees all of Sejin's memories and can feel all his emotions and the loneliness he felt. It was despair.
Ido felt guilty and avoided Sejin, and he only meets him at night when he is asleep.
Sejin feels neglected and lonely.
The doctor says Sejin is pregnant.
Sejin felt disgusted and didn't know whose child it was. He felt depressed and finally decided to kill himself in front of Ido using the gun.
Ido also killed himself, and voila, he's in the second timeline.
because some say it wasn't seme who raped uke, but the brother. But seme was still an asshole to him and that is why he committed suicide. Some say it was all seme, he bought the uke and just tortured him and then regretted when he committed suicide, which makes no sense. Why would someone clearly psychopathic like that care and regret and want to make amends? I am so confused. I dunno if I should just continue reading this urgh