Uh, Eri said the victim only cheated to get his wife's attention but man what was he thinking? Was it really such a good idea to cheat on someone who is an expert in judo and with a woman who's husband your wife admires?
Lucky the husband didn't find out the affair first. I doubt the victim would fair much better vs. Him.
Anyway, rare win for Kogoro to figure out the gist of the case without hints from Conan.