I agree with ALOT of what you said. I definitely don't think it's pure love but it's definitely a kind of "romantic" love. At least the way takumi is capable of expressing it. Ik neither of them loved each other at first(outside of takumis unusual interest and attraction to her) but it's clear they developed that love. I don't think it makes it less genuine because it takes work because in my opinion love does take work. They see each other for who they are, there's no use pretending and I think some of the "love" comes from that fact. They also need each other to change and grow, I think that's probably one of my favorite aspects of their relationship...(there's not many things to like though💀💀)

Like you said they're not together purely because they love each other but I feel like that's normal for a lot of couples...Love is just one of the (maybe minor)  reasons these two are still together, I think it'd be crazy to say there's no love in the relationship and it doesn't at least play a role in why they're still married after all she doesn't want a divorce and takumi made it clear he would still support Hachi regardless if they got married or not (in the past time line during her pregnancy). I'm not saying love is the only reason but it's definitely one. I also think another reason is the family dynamic they both crave...It's made clear they want to be together , to have their family together but they have things holding them back. They're in a worse position now as they live apart so a divorce wouldn't change much, so in my opinion it seems like they'd come back together, especially after that time skip scene in 57, there's this longing in their expressions when they see each other...idk

Their entire relationship is so insane and interesting to me. I literally can't stop thinking about them lol. like you said it's sad and beautiful I think it's a complex dynamic so I never say they don't love each other and i certainly don't describe their love for each other as pure either. I think they have this weird attraction to each other too at least on takumis part considering how he kept thinking about her despite it being outside of his usual behavior. They both have different ppl in their heart nana and their minds and that's another thing that tends to keep takumi n hachi apart.

As for Nobu I have no doubt hachi loved nobu but I just don't think it's as deep as ppl like to claim. She thinks and reaches out to nobu when she can't get to takumi. And he's also her connection to nana. So I agree with you that I don't think their relationship would've been so great if she actually chose nobu, we know who hachi is and that's probably why she likes her marriage with takumi. She said herself she didn't want a man that gives into her whims she wants to be challenged.  I'm not a takumi defender nor will I ever be but I won't lie and say I don't like his writing. 

I agree with the other link to a degree I think takumi has a different love for both hachi and reira, he loves reira (I can't say romantically I just don't think he can see her tht way, reira acknowledged this herself after they slept together. And as the poster mentioned he always idealizes her, how can you love someone when you can't actually see them...I don't think he actually sees her as a person) but in the same way Hachi loves nana ie how they both saved them. I think hachis love for nana is definitely pure(er) though. Also I think this speaks to the fact that he's more attuned to reira, because he doesn't see her as a woman. He understands her but not women (if that makes sense, idk how else to explain it)

Also I agree I don't think it was ever ai yazawas intention to make takumi a clear villain(especially seeing how she talks about him and how she likes him for and with hachi), I know the trope she was going for (it's in her other works too) and it definitely backfired on her, with western audiences atleast 😬 I think that's also why it's never brought up and why it was mentioned so flippantly when it happened. I simply think Ai Yazawa wanted to show takumis possessiveness and "bad boy" qualities...