"W-why can't I just tell him..."
I'm wondering about that, too. It's starting to look real artificial and forced.
W: "Why do you want to know so badly?"
A: "I-I don't know..."
Good grief. Please. Your words and actions have never truly lined up. What is this, I don't even...
I'm starting to dislike how it's Wataru again who seemingly has to do something. Aika may have realized a lot of things and felt very guilty about it, but without her taking action and saying things herself through proper communication she may as well not have grown one bit from the start. I still do want to see progress between them, but not like this. It's not very satisfying for me. Aika has not grown at all, because at the end of the day without applying any of the lessons she's learned, it's just all in her head.
Natsukawa keeps shoving the responsibility of sorting her feelings out onto Wataru, and the sister who has no idea what is going on keeps pushing for them to be together.
I'm not going to be as critical of the sister as others are, she is making mistakes because she doesn't have any of the information we have and just believes she's genuinely giving Wataru a helping hand, but Natsukawa gets no leeway from me, she is the one with all the information but refuses to communicate properly despite witnessing how much her lack of communication is tearing them apart and realizing it's her fault, yet she refuses to change and continues to seek validation from the guy she spent years rejecting!
According to LN readers in the anime comments section, the continuation from where the anime ended was just exactly what we had seen in the anime going for several volumes without any major changes. Given the manga's flow, it seems to be an accurate description, Natsukawa doesn't change whatsoever, and she doesn't let Wataru get over her nor tries to do anything for them to end up together!
As others have pointed out, every single girl is a better option than Natsukawa!