We've never sold the Expansion Pack through the Steam storefront for any period of time. I have confirmed with Steam that this is the case as of today. Please contact Steam Support directly for further clarification.
> But my actually question is if this DLC shows in my Steam Library, so I will get these 2 route DLC, right?
The Steam code you redeemed only accounts for 1 route (Fashionista) on Steam. We're splitting it into 2 separate DLCs for Steam due to the way Steam releases work; we cannot release half of a DLC alone and place it for sale, so their pages must be split OR we'd have to wait to release the DLC on Steam for several months past the itch.io release. And the latter would make no one happy. (Elaborating on why before anyone else asks about it. ;;)
Unless Steam adds a method for us to add the 2nd DLC to the key that was already given out in the meantime, the other Steam key will be distributed via itch.io when the DLC pages are split & approved.