I mean, I actually do agree that I want Miyagi to confess and turn dere as soon as possible, and I am anticipating something big soon as I mentioned before, but she has good reasons for trying to set boundaries and wanting a clearly defined relationship, and it can't feel great that Sendai constantly pushes her boundaries without giving her any sense of security in their relationship.
Love is a two way street. It's on both of them to define the relationship and both have valid (from their POV) reasons for keeping things ambiguous.
By pushing boundaries do you mean Sendai initiating intimacy? It's totally fine if Miyagi turns Sendai down when she starts making sexual passes at her, but what about casual intimacy? Like when Sendai gives hugs or kisses here and there and Miyagi often brushes her off?
Sendai has incredible fortitude, because if my "live-in situationship partner" consistently gave me the cold shoulder like that, I'd devolve into a spiral of negative thoughts regarding how my partner feels about me. That they're just putting up with me and don't actually enjoy having me around.
Also, damn, Miyagi really can't live down the running away accusations, huh? Can those who are caught up to the MTL not agree that she has grown past that, and very much demonstrated to Sendai that she has grown past that as well? Guess that one really stuck a nerve with y'all.
Unfortunately I can't yet agree we're past that because Sendai hasn't thought about how she's past that. Around 15-20 chapters or so ago in the MTL Sendai has thought about how she's afraid of having sex because she might tell Miyagi she loves her in a moment of passion. And she's scared of doing that because that might push Miyagi too far, causing her to abandon Sendai.
The way Sendai plays it cool all the time (even though we, as the audience, know better) makes it seem like she constantly has one foot out the door even if it isn't the case.
I've only vaguely been aware of this and kind of mentally wrote this off as Miyagi's abandonment issues from her mother being projected onto Sendai. I'll add it to the list of subtle things I missed when reading the MTL.