Well I think the title doesn't match bcs by the title and the start of manhwa he was supposed to help those two get together and they should be main couple. It's "someone else's" not "my bl Manga". Instead of concentrating on the first couple which should be main couple it concentrates on second couple more. Not that I'm not happy with it, I love both couples. Just the title doesn't really match.
I personally think the title clearly defines what the story will be about. The title implies that the main protagonist of the story will (not) have a love story but as given, it will be about him and his journey to finding his own love life. The other couple as you selfishly believed to be the main protagonists of the story are just plot drivers to show how the protagonist will move forward. Now that they are happy with each other and have nothing more to do with the MC, they are relatively irrelevant to the plot and we are now able to focus more on the actual protagonist. If it is about that couple, the title would have been very different because there would be no need to state the words, not my.
I think it shouldn't have turned out like this... The title doesn't match and I think it's not original storyline. Like where did suhyeok get that bruises from the start of manhwa when he was changing? I think the author changed storyline soon after that. I love it as it is but something just seems off