Whispers Behind the Wall (2013)

Martin leaves his protective parents’ home and comes to Berlin as a law student with high hopes. He finds a tiny, run-down flat in a strange, dark apartment block, from which the previous tenant has disappeared without a trace. Having no luck with social contacts at the university, Martin quickly falls for his mysterious landlady Simone, who lives just next door behind a thin wall. Hoping to find trust and intimacy, Martin loses himself in the house’s disturbing world of sex and violence. Deep in the walls, Martin discovers the true horror of his first love.

Source: TMDb