Honestly, don't most romance manga focus on the main couple until the end after they get together? To the point where the side characters don't get closure. Komi-san and My annoying Senpai being 2 examples of this, although to be fair, the Senpai one got axed and had to rush to a timeskip.
quite honestly, komi-san is the ONLY ONE i can think of (hell, i didn't even remember until you mentioned it; didn't read the other manga). either way, i want it more exactly BECAUSE it's so rare. you either get NOTHING (majority), a confession and it immediately ends with them holding hands and walking into the sunset or some shit, maybe a kiss if the author feels daring (a lot of the rest) and then the two examples you listed where it actually continues.