Ch 1-7.5 focuses on the first couple. As much as I want to call it "main couple", it's not. Because the second couple took a lot longer focus (vol 2 and 3 focused mostly on them).
The first couple had a fast paced relationship which they did admit (lol). After all, they got together in like a week or two. Despite that, it didn't feel rushed (in terms of storytelling), since they're just both too easygoing and went with the flow of their relationship.
The second couple is a tsundere x obsessed childhood friend. Which isn't my type at all (tbh, you can consider what the childhood friend is doing as sexual harassment). I don't like the childhood friend at all (too stupid, too much sexual advances, too less romantic advances). I didn't like the tsundere either (in his story. I liked him as a character outside his romantic entanglement lol), too tsundere. Soooooooo, I skipped. I mean, I read this like 5 years ago (up to 3rd volume iirc) when I still had low standards and I barely liked it. I'm glad I don't remember the story, but I won't let myself suffer again lol. And mind you, even in vol4 when they were already an official couple (or so I believe), they still act the same - especially the tsundere. I don't expect a big leap in character change, but damn, even a little growth would be appreciated, but you didn't have it.
Vol 4 is about a new tenant related to Haruto's past. And I hate him lmao, another tsundere, too stupidly childish. He's already a fucking adult and he didn't grow up even a bit. The only thing I liked is how Haruto grew out of his shell; gotta love his honesty.
The latter half of vol 4 focuses on all the tenants (too much spoilers if I say anything more). And I really love their familial relationship.
I would love to see more of the whole tenant family, but, alas, this is yaoi and won't focus on non-bl things.
Heart no Kakurega