Complex sentence: Harbouring passionate interests for Satanism and extreme metal, he was introverted in his environment, and left for Stockholm when he was 18, home to extreme metal acts such as Entombed and Dismember, whom Ahriman already knew personally.
Split into simpler sentences: Harbouring passionate interests for Satanism and extreme metal, he was introverted in his environment. When he was eighteen years of age, he left for Stockholm, home to extreme metal acts such as Entombed and Dismember, whom Ahriman already knew personally.