As the series goes on, you can definitely see the growth of the characters over time. Each one is more open to communicating with the others (at least, in the main cast. Their partners? Ew. Brother euuugghhhhhwwww). It shows how much they've realized that

a) Being with someone with a disability has challenges, absolutely
b) You cannot decide for others what challenges they are willing to accept
c) There are ways to find compromise in relationships rather than just shutting it down/breaking up/ending things altogether without communicating

You can also see the growth of the author. In early volumes some of the commentary around disability sounded very much like ableism, not just from side characters, but from disabled characters themselves. This wasn't "I wish I didn't have to deal with my disability," but "disability is such a detriment to the world around me, etc etc" in a way that was just so, so crappy overall.

Now, some characters are still ableist... for example, at one point the main character's mother says that she's glad she broke up with the disabled love interest and is happy with someone new, because she can now live a "normal" and happy life. While the daughter didn't check her mother on this (some of which is cultural), she did stop and think "wait... normal? What does that even mean?" and kind of assess the hurt that conveys. The ableism is checked now.

In the end notes, we do see that the author dealt with her mother's chronic illness when she was younger, and that it was a large struggle for her, and I do think that some of this is behind the negative feelings and commentary that surrounded disability in earlier volumes. Having this understanding also helps moving forward.

Tl;dr: this volume handles disability better than the ones that came before it, and as the plot continues to develop, the characters become more likeable in ways that make me want to continue reading the series.