First, the bad:

- The plot is not particularly fast-moving. I like slow burn, but sometimes it goes around in circles bit too much.
- Scene cuts. When you watch Ep 12, try to find an uncut version, or at least watch the cut scenes after you view the episode. For some reason, the LineTV broadcast cut the most important scene in the entire series, making much of the 12th and all of the final episode totally incomprehensible.
- The acting is uneven. It's not bad by any means. You do get a solid sense of who the characters are, and that's the most important. Folk, who plays the older step-brother, Prab, is a bit too good at being a smarmy dick, so he's not very likeable at first. He's even better at being the sweetest and most loving person in the world, so you're likely to adore him by the end.
- Subtitles. They're nowhere near as bad as So Much In Love, but at times they're confusing, not helped by references to scenes that have been cut.

The good:
- The main couple are so cute it killed me. If the bunny scene doesn't win you over, this show probably won't work for you.
- Everyone is gay. For some, this is a negative, but I liked a world where every single boy is pursuing other boys, and it's totally normal. I was half expecting someone to come out of the closet as straight, and be bullied by his classmates and rejected by his parents. There is only one heterosexual male character (alleged) in the entire series: Chol's father, and I have my doubts about him. Prab's mother should certainly never let him attend a parent-teacher conference at that school unaccompanied.
- There are no implausible failures of communication. People talk things through. As an example, I'll give a minor spolier. Prab and Chol have to visit their father in the hospital. Nick, who had been casually dating Prab, wants to come. Prab, concerned that it might bother Chol, asks for his permission, although not needing it. Chol's response is ambivalent, so Prab disinvites Nick to make sure Chol isn't hurt. That's it. In a "standard" BL, Nick would come along, Chol would be jealous and sulk for two eps, there would be several montages of good times spent together to bad music, before some crisis forces communication. In another case, a guy blows up unreasonably at his bf and stalks off. (Cue two eps of sulking, montages of good times to bad music.) He goes to class, cools off, goes straight to his bf and apologizes for his behavior, they discuss what happened, and it's resolved.

There are two central bits of drama - both are likewise handled with communication, empathy, and and love. I spent half my time staring open-mouthed at my screen wondering where all the sulking and montages were. It was really wonderful.

This is not the best BL ever by any means, but it's in my handful of favorites just because it was invariably a joy to watch. If you can be patient with it for a couple of eps, I don't think you'll be disappointed. If you like BLs where cute boys are cute to each other, this is a gold mine, because not only is it that, it's logically written and not full of fan-servicy elements. When people behave poorly it's understandable why they did, and they almost always recognize it and make amends and apologize.

I don't hesitate to recommend it. There will be times you'll ask "why am I watching this?" But you'll likely want to continue.

Note: Don't stress over the student/teacher thing - nothing bad happens.