
and I can see that the main couple are still acting like grade school kids and the douchebag brother is still around, sniffing after the female lead. Yup, I hate the female lead just as much now as I did 5 years ago when I dropped it.

hi i think ur misunderstanding something
The brother does not have feelings for his brothers wife like at all. he never did. He likes spending time with her bc shes one of the first ppl he's made friends with. Theres evidence of him not liking her such as his response to fl's question of why doesn't she act the same around him and her husband and he replies with something along the lines of 'obv bc Im ur in-law and he's ur husband'. Remember that the brother is a high school kid and so fl dotes on him. She sees him as a kid and he sees her ad an older sister. They have a very cute friendship. Some more evidence of him not liking her is when he thinks his brother is weird for confronting him about being close wit his wife. He also has no problem saying his relation with her which is an in-law. If he had feelings for her he would hide that from strangers.
As for the main couple acting like grade school idiots is bc neither of them have experienced love. Also bc of the way that they're relationship started their nervous taking next steps since they're relationship isn't built off of love or previous friendship from the beginning. They're very hesitant about each other boundaries and this is addressed as a point of conflict.
As for them being very fluffy and sweet and seemingly happy over small things is something that is commonly found in shoujo. If you don't like cute fluffy things and are looking for more mature and in depth relationships I recommend josei
You're lucky, ahole, that you're even in the story and that Shiki actually talks to you. I can't wait till you lose bigtime and bawl your crybaby eyes out.