i hope we're not doing the 'woman who likes mc sleeps with his friend after feeling that he doesn't like her' trope, though it's certainly being set up that way.
I'm kind of wondering if his friend Osaki dumped him there and then left. Now that's he's freaking out about it Osaki doesn't want to tell him and is using it as an reason to kick him into thinking of Hikari as an option.