Maybe she's following the curve of reality, which Namori is incredibly good at. Yui and Kyouko have known each other seemingly since their first cells formed, so the continuum of their bond is never broken. It's like a married couple where aside from occasional jive to keep things happy, most of what gets done is not that notable but punctuates in fine points.
If you watch the evolution of a marriage, you don't see big surges of romantic activity but many little events.
Ayano and Kyouko have something resembling new love. It's a source of substantial dramatic events, but they can't come that often or the partners die from exhaustion. I don't have a problem with Kyouko/Yui, but I simply haven't perceived romantic reciprocity in their relationship on Yui's part; Kyouko worships Yui and wants to carry it further and Yui worships Kyouko but is sunk deep in the refuge of games, coffee, and friends. Maybe I'm wrong.
Me, I believe in the "polycule" of Yui/Kyouko/Aylano/Chitose. Those arrangements almost never work for obvious reasons, but those three could pull it off because there's a complex web of attraction and concern there and they are all a bunch of openhearted sweeties.
