Ruben insists he doesn't need help and doesn't want to stay, but Lou and Joe think he needs help. Joe says if he stays he he has to commit to the program and will have no contact with the outside world, including Lou. Ruben refuses and leaves.

Why does Ruben leave Lou?

The more time he spends with her, the more he realizes that he doesn't have a place in her life any longer. While Ruben was desperately trying to get back to his past, Lou has moved on to her future. ... Ruben's future is left to the audiences' imagination.

What happens to Ruben at the end of sound of metal?

During the film's final scene, where Ruben eventually finds stillness in silence and finds his own acceptance as a deaf man; that is a direct nod to the conversation your character has with him, where you're talking about moments of stillness and the Kingdom of God.