likely-straight best friend
I thought in this case the manga artist was the likely-straight one?
The manga artist seems like the type who has no interest in romance or anything outside of work or creature comforts. The OL at least seemed to be into her boyfriend somewhat. Granted she didn't share his unambitious life-plan and wanted to take her career to Tokyo). I don't know. The friendship is not interesting and currently isn't romantic, and if it becomes romantic, it seems like it'd be one that's kind of unhealthy (one person doing it all, and the other skating by without a care).
I kind of prefer my adults in fiction to have some semblance of self-awareness, and the girl with the fiance either isn't gay, isn't attracted to her roommate, or is so self-unaware, she can be living with a romantic interest and not be aware of it.
I guess in my old age, I get tired of the "super-friendship yuri" where it's mostly about being neutered BFFs.