When Kazuya refuses to visit Haruka's grave it is not because he feels like it would be him being unfaithful to Chiho or disrespectful to Haruka, it is because the very last time he ever spoke to her she told him "this is my final wish, get out right now and never ever come see me again." And I would love to know how some twists "respecting someone's final wish" into "he still loves her and more than Chiho." Kazuya just happens to be respectful enough to honor the dying wish of his first love who only said it to him to be absolutely certain he would not chain himself to her after her death.

You can talk about motivations behind a love, but that's how it works in real life too. Especially in the beginning. The only truly selfless love you'll ever find is that of a parent for their children. Sometimes between siblings.
I don't think the ending was hammering home the fact that Chiho will always be second, even if only because people don't have a love ranking in their heads. It was to tell us that some feelings are so strong that they survive time, and there's no point in denying them. Accepting your feelings is the only way to live a happy life.

ones where you can never attain the number one seat in his/her heart.

You have the really cute sick girl along with the boy who has been supporting her all her life. Everyone knows she's weak, but she has kept the fact that she's dying all to herself. When it comes time for her to be hospitalized, she does the same thing as in the other similar manga. She follows the cliche perfectly by hiding the fact that she's dying from the boy and her friend and then she just stops coming to school due to hospitalization. But the way I feel about that, she owed it the boy who has supported her all her life an explanation and to tell him her real feelings and it's wrong to just disappear leaving the ones who care about you to worry. In the long run, she had every chance to experience true love before her death. She thought it would be worse on the boy if she told him how she felt but I think he would of been much happier in the end if she would of returned his feelings. It's a much better memory than being shot down over and over by the one you love. These stories wouldn't be so bad if they would break out of the cliche and tell something more original

Ok firstly the 'romance'. Kazuya has been in love with Haruka basically all his life, and even though she too likes him for both their sakes she keeps rejecting him, knowing since birth she won't live past 20. It's obvious that Chiho develops a crush on Kazuya, and it is later shown how the two slowly get closer after Haruka's death as they deal with their grief together. I felt the romantic connections for both pairs as hollow; Undeniably Kazuya loves Haruka, but it felt more like Haruka wanted someone to love, but knew she'd never live long enough for true love, so she pitied Kazuya and didn't date him. I'm not saying she had no affection for him, just she was more in love with the idea of love since she'd never get to experience it. As for the obvious problem with Kazuya and Chiho's relationship, well Kazuya still loves Haruka even after dating, marrying, and having kids with Chiho. I really think they'd be better off not together, and even with a 2nd child on the way they should divorce, but if they're happy with how things are ok.
I love how strong Chiho is, because she knows Kazuya still loves Haruka but can also make her own happiness...like the first time Kazuya tells her he loves her she softly smiles and replies,"In Haruka's place"