I just cannot finagle myself into believing that when Ianto looks up to Jack in tears and literally says, "You gave my life meaning again." that you can interpret anything other than crazy deep emotional attachment.

I thought about "you" as Jack representing Torchwood, but he's always had Torchwood, so that doesn't really fly.

And, as I said in my own comment, brains does not preclude anyone from falling madly into inadvisable and doomed love. Smarts usually only makes it worse because you know what you're doing while you're doing it, and can't stop yourself.