Funny enough I†˜m actually back from a work meeting we had just now about blackmail with encrypted data, but it seems they left out the whole banging part...
I'm pretty sure it's some kind of elaborate blackmail plan he came up with to have sex with her, and also, somehow I don't think that's the real reason the previous girl quit.
I mean...First, she coincidentally got said email the day he warned her about he, and he just so happened to coincidentally forget to take his pass with him and came back for it.
And of course, we get confirmation by that ending that he's basically just going to blackmail her.
I suspect by the time we get to Page 20, we probably discover the real reason why the last employee quit. And it didn't help when the last panel on Page 17 showed a strange look on Kawakura's face at the ... er, 'climactic moment'.
In the words of a certain screwy duck, Kawakura-san ... "YOU'RE DESPICABLE!"