I get why this manga can be a little controversial, since both main characters have a really codependent personality in this relationship. The trap here is that no-one in this world has a "healthy" relationship in all aspects, no-one has a "perfect" relationship so I can see this as a really human one. None of them are exactly bad people, and they lack communication skills as... most japanese people in this world XD It can be agonizing for us since we don't belong to that culture, but for them is not really that rare or unusual, so I get why the characters did what they did at the beginning of these relationship. I don't buy relationships that are about controlling everything about the other person, or "belonging" to the other person, but as I said this looks like a very real relationship in this world. I like that the mangaka could portrait this little toxicity without making any of them the villain or the bad guy. Really good job and I admire it.
Itonaga-kun no Koi no Ito