Well if your friend thinks your an idiot for knowing the difference between indicas and sativas, then I think we've got a clear case of the pot, the kettle, and someone calling the other black.

Just let him do what he is doing now, and once the girl realizes what is actually happening she'll dump him like that and your buddy wont have to hide his lifestyle anymore. In the meantime just laugh at how women can manipulate men without even trying.