The point of it stretching out is to show that not everything ends all honky dory with these stories.
It's showing the struggles and reasons behind them for both Megumi and Tsugumi. The conflict with Megumi's dad would have fell flat if it all ended with one volume leaving it to feel superficial. They had been building him up as this super prejudice Omega hater and it would have just been disappointing if it ended with them either going against his wishes or him suddenly "seeing the light" and accepting their relationship.
This was always going to be the main conflict. Everything else was just building it up to show that the resolutions aren't always easy.
Also, I don't get ya'll at all. I'm constantly having to explain WHY bl mangaka are constrained to one volume series 'cause everyone is consistently bitching about them being too short. Now we've got a series that is fleshing out family backgrounds and their conflicts and now ya'll wanna bitch it's too long?? Pick a fucking struggle lol
The first volume was a masterpiece.
The story should've ended there because everything that follows—especially the sexual assault by that 'friend'—feels completely unnecessary. This might be an unpopular opinion but I genuinely believe that many BL stories shouldn’t stretch out over so many volumes and seasons. Not all of them manage to maintain the same quality of storytelling as in the beginning. Nevertheless, this manga still holds a special place in my heart because I love the two main characters and the first volume is just so well done (づ￣ ³￣)づ