
I kinda wonder if Eiji and his brother know that Reiji is their uncle. No one seems to really mention it. I also feel bad for the dad, being in love with Reiji this whole time, but having to marry his sister instead. And although he loves his sons, I assume, he didn't completely love their mother. Well I'm glad everyone's got their happy ending now.

There's a reason people don't though, it's common knowledge that people didn't marry for love for, or even affection until very recently. They did it for security, for society, for tradition.
I was born in the 90s and from a traditional background, my parents did not marry because they loved each other, I don't even think they liked each other, they just made the best of what it was. The thing is that a lot of our grandparents, if not our parents, were born without the luxury of choice in marriage. And in traditional countries and/or traditionalist families, this is sometimes still the case, and yet we do not talk about it either, it's uncomfortable to discuss someone's lack of choice after all. Food for thought :)

Me too, I'm from a very traditional family, and most of the members are married because of convenience. My parents do not "love" each other but they got along pretty well. I'm not obligated but I'll probably marry in the same conditions. Since I'm not a romantic person, I don't mind as long as my partner give me monetary stability and treat me with respect. Still, I feel sad for those that do want to find love and don't have another option :( sorry if my english isn't good.

Well the same goes for me. My parents were arranged to be together, my sister was, and I'm sure I will too. My sister seems fairly happy, though I admit I don't know about my parents anymore in recent times. But I think they did love each other back then. And honestly, as their child, I want to believe that they love each other. That's why I feel bad for the dad and his kids. Especially when Eiji realized his dad may not have wanted to marry his mother. I don't think a kid would want to think about that. Though I will admit, I guess it really didn't occur to me that some people who were arranged to be married don't necessarily fall in love.

To your last point, I think it depends on the kid, and how sensitive they are to those emotions. You seem to be, going off of only these two comments, mind you. I can only guess, but I assume you are also slightly more romantic in nature than myself.
I was born not into a 'happy' family so much as 'functional' one. Their relationship worked, for a time, and then it didn't. This doesn't bother me, and it didn't bother me as a child either. I admit I did feel sad when my father left the house, but only because I understood that I could no longer have both my parents with me at the same time, not that they weren't together. This was the extent of my experience of their relationship dissolving, they are much happier apart, so the inconvenience of not being able to have them both (as a child) is a non-issue now.
Consider also, how these kids would have been socialised. They are (depicted as) living in a more hierarchical part of their own society, and much more likely to understand the pressure that their father's position entailed. Eiji is not likely to feel remorse as a product of his parent's marriage, then he is to feel remorse at his father's missed opportunity "does that mean you didn't choose" http://www.mangago.zone/read-manga/houtou_musuko_to_sewagakari/uu/houtou_musuko_to_sewagakari-chapter-5/33/ He even says that he doesn't want to hurt his father by asking that question, which implies that he assumes, correctly, that his father did love someone else, but had to leave them behind in order to fulfill his duty to his family.
That being said, I can only assume that the more romantically inclined you are, the more likely this particular situation would bother you. And like yourdissapoitedmom said, we feel sorrow for those who want love, but for one reason or another, cannot have it.

Haha. Very true, we tend to realise after the word is said, but not as many are willing to admit that they may have spoken too soon :)
Happy to discuss characters and storylines anytime!
Gahhh I understand Masayuki's clean-freak tendencies so much! I freakin hate it when people leave their dirty clothes all over the place, or when friends touch game controllers or remote controls with greasy hands! In my case, I acted kinda playful when trying to get my friends to wipe their hands before touching my stuff, but at the same time let them know I was serious. Not saying that would have worked for Masayuki, but I was thankful my friends didn't get too annoyed at me for it.
I need you in my life I'm lazy at keeping things clean and neat, but if someone forces me to clean I do a damn good job at it. (And that happens maybe once a month)
lollll ok, here goes! PLEASE CLEAN YOUR ROOM ASSUMING YOU HAVEN'T DONE SO YETT! :D lollll I know I said I acted playful with my friends, but if I have to deal with it long term, I can get pretty vicious lolll I'm probably a terrible source of motivation to get someone to clean. xD
Actually I'm very thankful as RIGHT NOW I'm supposed to be cleaning because we'll have visitors coming later today, so I guess I'll leave yaoi mangas alone for now and start cleaning. What a great timing, thanks!
Loollllll! Glad to help! :D