Complex sentence: It was only when he learned that Angélique was going to marry her cousin, Philippe, this ambition was a final blow to his impressions of her, gave up as her suitor, left the chocolate business and rejoined the army.
Split into simpler sentences: It was only when he learned that Angélique was going to marry her cousin, Philippe, this ambition was a final blow to his impressions of her. He relinquished his suit, left the chocolate business and rejoined the army.