when someone tries to join me it says: ''the game session is no longer available''
And if I try to join someone else it says it aswell.
What the fuck is going on?!
Just go back to multiplayer menu and back, Its a common issue not something caused by the update.
I'm assuming they haven't downloaded the title update.
Tell the players in your party to go back to dashboard and clear their "system cache" to download the title update.
They should be able to join after clearing their system cache.