It'll be an unpopular opinion since romcom comments usually beg characters to "just get together," but IMO, this type of series was better suited for more teasing and courting.
I think having an older crush on someone who isn't a relative but is close to the family is relatable to many of us bois, so series like this really hit a soft spot. But the most interesting part isn't really the boyfriend-girlfriend experience (which is going to be just a normal one anyway), but rather the situations that arise from being constantly close to someone who isn't family. In this case, Hinako visiting the house or the three-way dates with Tsukiko are great setups for doki doki moments.
IMO, the MC having a one-sided crush (or anyway Hinako being unintentionally teasing and cute in third person instead of directly reading into her feelings) should have lasted longer. But this was almost never a thing since the serialization used the one-shot as a basis instead of restarting, which IMO was a mistake. So it went directly to phase 2, with her being openly in love. BOTH characters being constantly bashful or insecure can be frustrating, so them basically dating is better. But at the same time, the manga's gimmick (Hinako being the older sister's friend) becomes irrelevant and it turns into a more generic "I'm dating my upperclassman" series. Which is ok, but feels like already seen.
Anyway, overall it's an enjoyable read so far, it has very cute moments and hope there's room for more. My favorite Hinako panels have to be when she's shown jealous and possessive though. The part when she gets jealous of an elementary schooler for playing in the park with Asahi is the funniest bit of the manga.