Definitely an unpopular take, but one that I absolutely agree with:

I’ve honestly been afraid to say this myself, but I don’t think they loved each-other as the story progressed. In the beginning, when they first met, the love was definitely there, but in an unhealthy, borderline obsessive manner. I’ve always thought of them as people who were afraid to loose, so they cling to each-other. As a habit, Nana mindlessly goes to Ren when she’s struggling; It’s almost like she can’t find another way to cope, which could definitely hint to an obsession, as you said. I think the reason Nana claimed she went to Tokyo not for Ren is because of her pride, like she didn’t want to be looked down upon for wanting to be with him so badly. I do agree that she loved Hachi, too, and that that was her reason for wanting Hachi and Nobu to stay together.