That last panel catches you by surprise

For some reason, I always liked girls with abs... This just feeds into that.

That last panel makes me suspect that Matsukawa was cracking a joke. That is, the "boyfriend" is actually Senpai, and she's making fun of her masculinity/tomboyishness by pretending that they're not in a relationship and saying that she (Matsukawa) has a boyfriend.

I want to believe this, but Senpai's internal monologue makes it seem like that isn't the case.
;~;7

this is sad man:(

https://dynasty-scans.com/chapters/secret_in_the_office_kitchen#2

I think this needs the BISEXUAL tag.....