Complex sentence: Stein spent a number of years living in Paris with his sister, however, in 1914, the two split due to Leo's resentment of Gertrude's infatuation with Alice B. Toklas, a woman he described as "a kind of abnormal vampire".
Split into simpler sentences: Stein spent a number of years living in Paris with his sister. In 1914, the two split due to Leo's resentment of Gertrude's infatuation with Alice B. Toklas, whom he described as "a kind of abnormal vampire".