She is in love with another man. These are two separate people in her mind. It's up to Ishizumi to come clean. At least author seems to abandoned the idea of boss getting flustered with day time ishizumi.
You're getting way ahead of yourself, it could easily still go down that route. The author goes for funny scenarios more often and having her go crazy thinking she's into two different guys while it's just one is a very Japanese joke set up.