@Kuroageha
I totally agree with you that his decision to bring Honma to the café basically brings his chances down to nil. Honma, however, is the only person introduced in the manga so far that's an adult and also shows any interest in Kosuke (as heavily implied from ch 20 when she is introduced and up until the big incident in ch 26 when she defends him against his daughter). The one seemingly societally acceptable route out of this mess is there, but he doesn't know she's interested in him and then subsequently ruins any chance of even going down that path. But the path exists, even if only briefly. And unfortunately, the author uses this one potential path out (Honma) and Kosuke's pushover personality/stupidity (probably doesn't help that he's been drinking and deep down he wants to see Kisaragi) to instead crush our hopes of salvation for Kosuke, bringing more drama and suffering upon him.
After the incident in ch 26-27, Honma does feel guilty for causing harm to Kosuke's relationship with his daughter (plus the dramatic irony of how Honma defends Kosuke, just rubbing salt into his wounds because he hasn't been acting like a good father/person) and also probably creeped out that he's in love with his JK daughter's friend (Honma also probably thought Kisaragi was someone of age). Furthermore, because she's a new employee that could have potentially helped him at work, the straining of this workplace relationship only adds to the pile of Kosuke's burdens.