I think the name Moratorium, as stated in the end of the chapter, pretty much explains this whole situation.
I interpret it very differently than you. For one thing, "Moratorium" originally consisted of just two chapters, the third was added when the series was republished in the Cocytus collection. In that sense, I think it is more likely that "Moratorium" applied to Mao in the first two chapters, and her decision at the end of the second chapter is the end of her moratorium.
In the usual sense of the word, it would be the end because she gets a proper job and becomes a full-fledged adult.
I think its application to their relationship is similar. Mao was stuck in uncertainty, not really knowing what it was she wanted, or how to get it. Her job search was going poorly. She knew she would be separated from Itsuki. She had no other friends or people she could rely upon.
Then, she finally resolves herself and decides that she wants to be with Itsuki forever, no matter what. She works hard to make that happen. In this sense, "growing up" means working hard and sacrificing her uncertainties, her moral qualms, and any empathy for Itsuki in order to pursue her goal.
It could be then that the most recent chapter is about Itsuki's "moratorium". However, Itsuki is quite clear that she is manipulating Mao. The lines, "if she's afraid of losing me, she'll jump into my embrace on her own", "did you think you were the only one who could be cunning?", and "I was getting a drink with a coworker" (echoing Mao's earlier excuse), make clear to the audience that she is putting on a performance in order to make Mao desperate.
This would then be an echo of the first two chapters - Itsuki has been stuck, unable to do anything, but she finally resolves her doubts. She decides that, above all else, what she wants is Mao. That line in the shower has two parts: "After that [Mao holding on to me], there's no way I'm giving up [on her]. Nor will I settle for just idly staying by her side." She cannot give up, and she will not stay as she is. She is committed to making Mao hers, and executes a plan to achieve this.
We do not know how long they will stay together, or what form their relationship will take. However, it is clear at the end of the story that neither one of them intends to let go.