Complex sentence: By early 1890, Van Gogh's attacks of illness worsened and he concluded that his stay at the asylum was not helping to make him better, which led to move to Auvers-sur-Oise just north of Paris in May 1890.
Split into simpler sentences: By early 1890, Van Gogh's attacks of illness worsened and he concluded that his stay at the asylum was not helping to make him better. This led to his plans to move to Auvers-sur-Oise just north of Paris in May 1890.