Here you go.

For those who didn't get it, the night that Sunggyu and Woohyun met on that bridge, Sunggyu was not trying to kill himself.  In the flashbacks throughout the story, you find out that Sunggyu is actually the leader of the Jin Yong clan.  They had a battle with the Do Hun clan (Hoya's clan) however Hoya and some members were not there at the time, hence why they survived and wanted revenge.  With his sword in hand, Sunggyu gave chase.  The leader of the Do Hun clan jumped off the bridge trying to escape.  Sunggyu was about to jump down after him but Woohyun came and stopped him, thinking he wanted to kill himself.  Sunggyu dropped the sword he was holding over the bridge and turned around to see Woohyun.  That night, Woohyun said that he would marry Sunggyu so that Sunggyu can be his wife.  Yes, wife.  Woohyun thought he could be seme.  That's why Sunggyu laughed because he thought it was funny that a boy younger than him wanted to be his husband.

In chapter 1, the boy helping the woman is Myungsoo.

In chapter 3, the one who returned to his apartment is Myungsoo.  The intruder is actually the messenger who has come to give him his next target to kill, Mr Park, the man who just had dinner with Sunggyu.

In chapter 8, the men that Woohyun was trying to hide from are the people his parents owed money to.

At end of of chapter 11, when Woohyun rushed up those stairs, the people waiting for him were the men who his parents owed money to.  His apartment was turned upside down by those people.  They kidnapped Woohyun because they saw Sunggyu driving him home and knew that Sunggyu was rich so they wanted a ransom.  Sunggyu arrived later to find the apartment in this state.

At the start of chapter 12, it was Myungsoo's apartment and he was the one who threw the knife at the intruder, the messenger.  His next target was his father, that's why he asked "Why him?"

At the end of chapter 13, Woohyun says 'It would have been better if you did not let me into your home' because he's worried that the loan sharks would come after him and that would cause trouble for Sunggyu.

In chapter 15, we find out that Myungsoo is the young master however he lives alone in the apartment because he hates his father and thinks it's not his real father.  That's why the two men had to come and pick him up to go see his father.

In chapter 16, Myungsoo kills his father and the bodyguards and then inflicts wounds on himself to avoid suspicion from the police.

In chapter 17, the figure is Myungsoo in the hospital room and the one who approached him is Hoya.  Myungsoo's self inflicted injuries aren't life threatening but with the help of Hoya, they are able to pretend that he was badly wounded.

At the end of chapter 20, Woohyun came down to the foyer after Sunggyu because he went to see the doctor and asked about Sunggyu's medication.  The piece of paper he was trying to hide was the prescription because he knew Sunggyu refused them earlier.

In chapter 21, the call that Hoya made to Sunggyu was a setup by him.  Hoya used the higher ups to get the officers to take Sunggyu in for questioning so that he could send Myungsoo to kill him.

In chapter 22, Sungyeol arrived late because Sunggyu sent him to the hospital to check on Myungsoo.  Sungyeol reports that the officers guarding Myungsoo's room were killed and Myungsoo was missing.

In chapter 24, we find out that the reason Hoya wanted all those men dead was because they were all members of Sunggyu's clan.  He wanted revenge for his own clan, even lying to Myungsoo so that he would kill his own father who was also a member of Sunggyu's clan.

In chapter 25, the person in the bed was Sungjong and not Woohyun.  Guess who the traitor is.  The traitor and the messenger who always came to Myungsoo's apartment is the same person.  Easy, right?

Also, the boy in the ICU is Myungsoo.  This time is for real.  Wonder if Sunggyu knows?  The hostage being tortured in the basement is Hoya.  Sunggyu is the one that came to see him.  He wants to know the whereabouts of Hoya's boss.

And finally, guess who killed his parents?  It was the reason why he lost his memories of that night.  Bonus points if you can figure out why.  Or I might write a sequel.