On September 21, 1780, General Benedict Arnold betrayed his country when he gave the British information that could allow them to capture the American fort at West Point on the Hudson River in New York. 
The short story is that “he hungered for money to support the lifestyle he enjoyed with his young wife, the beautiful Peggy Shippen.” 
|Peggy Shippen and Daughter (Sir Thomas Lawrence)|
Here are the highlights of the life of a man of turpitude.
1741, born; the great grandson of a three-time governor of Rhode Island
He received a fair education but was not studious, and his youth was marked by the same waywardness which characterized his whole career. 
1756 (age 15), runs away from home to join in the French and Indian Wars
1762, parents die; moves to New Haven, opens drug store and bookstore
1767, marries Margaret Mansfield; has three sons
1775, as captain of Connecticut militia, proposes expedition to Crown Point and Ticonderoga, must share command with Ethan Allen from Massachusetts; gets knickers in knot
June 1775, Mrs. Arnold dies
July 1775, “He went home to Connecticut in disgust.” 
Late 1775, passed over for promotion
1775-1778, promoted, leads wildly successful campaigns, screws up
May 30, 1778, signs new oath of allegiance to fight for independence
? Proposes to Betsy DeBlois
? Meets Peggy Shippen, 18 year old daughter of a Loyalist; breaks engagement with Betsy; introduced to Peggy’s friend, Major André
April 1779, marries “the beautiful Peggy Shippen”
May 1779, begins talks with British Commander, Sir Henry Clinton
Fall 1779, asks Clinton for too much money, Clinton refuses; breaks off talks with Clinton
December 1779, court marshaled for various screw ups; all but two charges dropped
January 1780, guilty of using military resources for private gain; rebuked by George Washington
? Asks for command of West Point; granted
September 21, 1780, meets with André– now an aid to Clinton– gives him layout and information of vulnerabilities of West Point.
September 23, 1780, André captured (later hanged); fleas to a British ship
— 1801, fights against Patriots, lives miserable, unhappy life in England
He gradually sank into melancholia, and died in London June 14, 1801. 
1 William J. Bennett and John T.E.. Cribb. The American Patriot’s Almanac. Thomas Nelson, Nashville. 2008.
2 The Encyclopædia Britannica: A New Survey of Universal Knowledge. Encyclopædia Britannica, Inc., Chicago, London, Toronto. 1955.
3 The Encyclopedia Americana: Complete in Thirty Volumes. American Corporation, New York, Chicago. 1952.