Complex sentence: But when Aunt Dahlia tells him that Angela has broken off her engagement to Bertie's old school friend Tuppy Glossop, he realises that his place is at her side, and goes to Brinkley.
Split into simpler sentences: But when Aunt Dahlia tells him that Angela has broken off her engagement to Bertie's old school friend Tuppy Glossop. His place is at her side, and he goes to Brinkley.