You're right! Tons of hints all through ch 2 of him at bare minimum flirting with a ton of guys at work, but probably sleeping with them all. Aww man. Sleep around all you want but you really shouldn't shhh where you work and live, esp when your friend gets you that job and he works there too. That's just begging for trouble. I'm kinda disappointed like others below, I was hoping for a light and fluffy feel-good story.
In the end of reading ch 3 I highly hope that is not mio! Because Shino just "hear".
But after I read your comment, it really makes sense. And its true, look like in the ch 2 tells us some "sign" about that. And now I feel heavy ╥﹏╥
Ugh, I don't wanna imagine but there's a possibility. Also, I kinda think Aoyama knows that Mio likes Shino judging by the way he treated Shino during the meeting. It would be pretty fucked up if Aoyama or Mio intentionally chose the toilet knowing Shino is there.
Honestly at this point I think they both chose knowing he was there.
I reread chapter 2 and i just noticed that Mio is really like that or it could be just my imagination going wild ╥﹏╥
http://www.mangago.zone/read-manga/crackster/mf/manga/crackster/c002/pg-9/