This manga is absolutely garbage, the story would be over in 15 chapters if the brother wasn't such a fucking indecisive moron, and most of the chapters by the end were absolutely unnecessary, can't believe I wasted 3 hours reading this shit.
You could remove the unnecessary infidelity misunderstanding and Kei-chan should have decided waaay earlier to stop whining and being proactive instead of living his own life in autopilot. It is also a bit underwhelming, although understandable, that they never really face their mother and just run from home a second time. The bittersweet ending fits the story.
I dunno if it's the style of dialogue or the seemingly nonexistent proofreading but it's sometimes hard to follow what's happening on some chapters.
Edit: Wow this is frustrating to read through. Koutarou seems to only exist to hamfist drama into Akira and Kei's relationship. Such an unnecessary arc.