Complex sentence: After the visits to the Kaiserkeller their relationship became purely platonic, as Astrid started dating Sutcliffe, who was fascinated by her, although she always remained close friends with Voormann.
Split into simpler sentences: After the visits to the Kaiserkeller their relationship became purely platonic, as Astrid started dating Sutcliffe, who was fascinated by her. But she always remained close friends with Voormann.