In the manga at some point even Toshio starts suspecting that Hitomi is one of the Cat's Eye, and Hitomi asks him what he'd do if it was true. Toshio's answer? They'd just go somewhere else and forget who they were before, and start a new love story.
At the end of the manga, it actually happened: Hitomi confessed being one of the Cat's Eye little time before she'd move to the US, and Toshio just asked her to wait a few days for him so he'd be able to come too. But when he arrives Hitomi has completely lost her memory of the past due a meningitis and is scared of anyone but Toshio, and, as Toshio told her earlier, they started a new love story.
At one point in the manga one of the Cat's Eye (Hitomi with her hair dyed blonde and green lenses) started trying to seduce Toshio so he'd become an accomplice. Toshio was visibly attracted from her... And choose Hitomi each and every time, even renouncing two chances to discover the secret of Cat's Eye.
At the end of the manga the Kisugi sisters leaving for Los Angeles right after Cat's Eye officially retiring and Toshio leaving the police to reach them right after that makes the rest of the Anti-Cat's Eye Special Team understand that the sisters are Cat's Eye and Toshio found out but didn't arrest them. Did they arrest him as an accomplice? No: they intercepted him at the airport and wished him a good life with Hitomi.