Yes, chapter 12 of the side story was the last one! I can confirm this because I also saw the Korean version and that says "End". There was probably a translation error in the English version. Indeed I read a comment at the time saying that in the official platform it was then fixed and re-uploaded. I understand the confusion because it's an ending we can consider "open", but if you think about it that was the best way to end the story. Given the genre we couldn't expect the classic happy ending. As you said, it is implied that they'll continue to live together and Sehyuk will continue to protect Hamin, basically they'll go on with their usual life.
And here I was stupidly waiting for the next chapter and keeping this on my tab so I know a new upload's out
I always knew it was an error by the translation team because I saw the Korean version first, plus the uploader of this website put "The End" in the chapter title which gave me extra confirmation, but it's in fact really misleading for those who don't know... if I were the uploader I would've just cut out the "To be continued" part at this point, and people would know from the chapter title that it's the end...
Side 12 is the end? It’s not a bad way to end the story since it pretty much ensures that they’re gonna be together for life lol
It’s just that the last “to be continued” panel left expectation that there was going to be more TTvTT