Story setup and payoff were in disagreement here

What l think leaves readers with mixed feelings by the end of this comic is that the story set up at the beginning is not the story we got in the end.

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At the beginning of the story, Jungyeon and Sunwoo are introduced to each other, where Sunwoo is the younger, socially-awkward son of the man Jungyeon's mother is remarrying. These are the first two who get screen time together, and this is the first plot point that is explored. First off, this is totally by itself a Marmalade Boy setup where the expectation is that these two ("siblings") will get together in a romantic relationship. And then the story goes on to painstakingly have Jungyeon try his hardest to pull Sunwoo out of his shell, while feeling more and more comforted by Sunwoo's quiet consideration and care of him. Classic setup for an in-family romance.

Meanwhile, we find out not much farther into the story that Jungyeon is in a relationship with another man, Hyunjin, and Jungyeon is insecure because he thinks Hyunjin doesn't like him that much despite Hyunjin acting like a low-key obsessive, crazy, yandere stalker. This is confusing since these two perspectives of the same relationship don't really agree with each other about what the current state of their relationship is. But it's clearly presented as not-good for Jungyeon. This usually signals that a break-up is needed somewhere later in the story, so the audience is now expecting it.

Also, normally, the reveal that a male character has a boyfriend (not a girlfriend) is BL plot-signaling to get the perspective character (in this case, Sunwoo) to think about dating same-sex, something he would never have considered before. Again this sets up Sunwoo as someone who is intended to the be the focus of the main romance.

It is also worth mentioning that Sunwoo had enough perspective chapters and screen-time to be considered on-par with Jungyeon, making him very clearly the secondary lead. Both of these characters have way more screen time than Hyunjin gets. Hyunjin is generally treated by the story as a supporting character, at least for the first 2/3 of it.

So, with all this set up, we're expecting that by the end of the story, Sunwoo's confidence will have improved to where he finally stands up for himself (and/or Jungyeon) against Hyunjin, causing a break-up, after which Jungyeon and Sunwoo's love for each other will be confirmed. This is the basic conclusion we, as the audience, are promised.

But instead, we get a story where the Jungyeon stays with his original boyfriend, Hyunjin, who is actually a good person, and our second lead, Sunwoo, is left with no boyfriend, not even a potential love-interest, and let's be honest here, has no wrap-up at all romance-wise.

The setups that did have payoffs were that Sunwoo's confidence did increase to where his social anxiety is reduced to more normal levels and he can interact with people now and stand up for himself now, but he didn't really gain anything from it (he actually lost everything he wanted from it). And Jungyeon, tired of being in a nebulous, unclear relationship, finally has a relationship that is stable and committed, even if it's not with the person we're lead to believe it should be from the setup at the beginning of the story.

There really needs to be a set of side-story chapters or spin-off story that wraps up Sunwoo's love life. Something that takes the things his character learned/gained in this story, and uses them to help him get past relationship hurdles in the new story. He'd actually be a great flat-arc lead for a spin-off story.

Anyway, all this is to say, this is why this story might leave a bad taste in your mouth, or leave you with a really confused jumble of emotions by the end of it. The story leads you to believe you're reading one type of story, then pulls the rug out from under you about 2/3 of the way through and ends it as a different type of story. Setups without proper payoffs are bad, setups with incorrect payoffs are bad and confusing, this is not any kind of clever subversion of anything, this is just immature writing. I will give the author credit though, (s)he did a brilliant job with the awkward tension at the end of the story and the almost slasher-style horror tone of the scenes where Sunwoo and Jungyeon begin to realize what a horrible train-wreck has begun unfolding.

Well, then. Just to be a completest on the topic -- A comic where this sort of setup is done well (probably) is "Love or Hate" (incomplete, but seems to be circling toward a conclusion finally).