Complex sentence: Peggy Shippen may have instigated the correspondence between Arnold and Major John André, her friend and previous suitor, who served as aide-de-camp to General Henry Clinton; she may also have been sending military secrets to the British before she married Arnold.
Split into simpler sentences: Peggy Shippen may have instigated the correspondence between Arnold and Major John André, her friend and previous suitor, who served as aide-de-camp to General Henry Clinton. She may also have been sending military secrets to the British before she married Arnold.