I found out this after I became a paying customer. But it's no biggie, because you can just download the music on which you want to listen to, and then your girlfriend can then listen to music via being connected to the internet. However I do believe that you have to be disconnected from the internet to listen to your offline play, at the same time as your girlfriend listens to music via being online.
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Well it would be great for Spotify to had some type of family plan. People with family's would love this have have no problem playing an extra 5 bucks a months to allow 2-3 devices to to use at the same time. Several other streaming services do it and would add to Spotify's customer base and profit margin. They could call it "Spotify premium plus" someone in Spotify try to make this happen your customer would very much appreciate it.
It's BS I have three daughters and I'm not going to get them each a account but every time my daughter play music it changes mine on my iPad. As soon is my yearly subscription is up I will say goodbye to spotify. And hello to BeatsbyDre. Now that it's own by apple they will allow family subscriptions.