I think you are pretty close. To add to your summary....
There are things missing on the English side and there will be two things reveal in Chapter 21 about Miha. The English translation of the summary does not have what the Korean and Spanish summaries has. Miha is 8 years older than Rihan, Sohwa, and Geum. Miha in the Spanish and Korean version of chapter 21 will say he is 28 and born January 1st. Making Sohwa 19 years old from chapter 1-5 then from chapter 5 and on Sohwa is 20 years old. So I hope Miha was not in a sexual relationship with Sohwa since his teens.....
Chapter 12 (page 13-15) indicates Miha and his sexual relationship with Sohwa started after Rihan left. But Miha has been in love with Sohwa longer than 3 years because he has been jealous of Sohwa and Rihan relationship when Sohwa and Rihan we’re together. I don’t think Stockholm syndrome complex fits. Since some comments made here I have been researching Stockholm syndrome.
They may not or may be half-brothers. Maybe not because Miha doesn’t look like them.
With generalized amnesia they can lost all memories or have some. I think from how Sohwa knew a friend things,(like he knew he had sex with Miha) he had to have some and there were times he act like his original self. But he gains most or all his memories after Miha leaves him. It is not said so we don’t know.
I don’t think we know why Chungha and Geum stabbed Sohwa and going after Sohwa (and Miha). I was thinking something else. But you could be right, it could be mafia related.
Oh! Since the date is November 17th, Sunday (Miha’s phone chapter 19) and Sohwa woke up on his birthday 2 weeks ago. Miha will be 29 in less than two months. It could be possible Sohwa is 20 years old from chapters 1-5 and 21 from chapter 5 on.
just me explaining the plot of what i remember since some people are a bit confused...
Miha (orange-haired dude) and Sohwa (black long-haired dude) have been in this weird two-sided abusive-obessive relationship for years ever since their teens a few years after they were introduced as step-brothers. Their dad hates Miha because he is from a past relationship, so he let's Sohwa do anything to him.
As a result, Sohwa is abusive and Miha develops a weird Stockholm-syndrome complex where he still loves Sohwa even though he regularly hurts him. Miha frequently dreams of leaving, and he almost does until Sohwa is stabbed one day and goes into a coma. So, Miha stays and when Sohwa wakes up, he has forgotten everything that's happened between them and loves Miha. Miha doesn't tell him anything so Sohwa is under the impression that they are just normal people who could be lovers.
Things are kinda stable at this point until the two go to a café where the kid with short black hair and the other guy with the orangish blonde hair (the one we saw in this recent chapter) talk to Sohwa and Miha. Miha is given the idea that Sohwa and the black haired kid were boyfriends before Sohwa had his amnesia (although this is never proven/confirmed yet). This makes Miha insecure and scared because he never knew. They argue a bit and Sohwa and Miha leave the café. The other two guys talk for a bit and the black haired kid wants to "take care of" both Miha and Sohwa. They decide that black haired kid gets Sohwa and the other guy gets Miha. The black-haired kid mostly does the talking, and it can be assumed he and the other guy are possibly dating already.
Meanwhile, things have become more tense with Miha and Sohwa, not only because of those two guys but also the presence of Sohwa's bestfriend from school. Sohwa thinks he's a rival even though the bestfriend has no interest in Miha. Miha is also scared that he is ruining Sohwa's relationship with his boyfriend (which he thinks is the black-haired kid), and so he asks the bestfriend if she can stay at his place for a bit while he decides what to do next. The bestfriend agrees.
While Miha is staying at the bestfriend's place, Sohwa manages to regain his memories but doesn't tell anyone about it. The bestfriend goes to see Sohwa and they talk about the relationship between Sohwa and Miha.
As that happens, the other orange-blonde haired guy from the café comes to talk to Miha at the bestfriends house. This is possibly to "take-care" of him as mentioned in the café in chapter 14. That's where we are now.
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Also stuff I couldn't fit, Miha and Sohwa's dad is an important figure in the mafia. This is why Sohwa is stabbed because he is supposed to take over after his dad retires.
The orange-blonde hair guy is the son of the long white-haired man that is seen talking to Sohwa's dad in the recent chapter. It is implied that Sohwa's dad and the white-haired man may have a sexual relationship.
The orange-blonde hair guy also met the black-haired kid in one of these interactions between the dads because the kid used to work as a sex-slave for the mafia. It can be implied that the orange-blonde sees similarities to the black-haired kid in Miha, which is why he seems nice right now. But he is most-likely just going to use Miha, as said in the café.
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That's all I remember! Sorry it's so long. Hopefully it helps. Also sorry I couldn't remember names, I usually just remember hair color.