He lied and said he planned to divorce his wife to keep the captain hoping for something more. And he started flirting with other women in hopes that the captain would leave quietly, he said.
Sinclair said his actions were "not based on my honest feelings for her, but were based on my fear of exposure."
Prosecutors have not spoken outside court since the plea deal was disclosed over the weekend.
The Army's case against Sinclair started to crumble as questions arose about whether his primary accuser had lied in a pre-trial hearing. It was further thrown into jeopardy last week when Judge Col. James Pohl said the military may have improperly pressed ahead with the trial to send a message about its determination to curb rape and other widespread misconduct. Under the military code of justice, the decision was supposed to be decided solely on the evidence, not its broader political implications.
Capt. Cassie L. Fowler, the military lawyer assigned to represent the accuser's interests, declined to talk about the case outside court Monday. She referred questions to another attorney who advised the woman, retired Navy Rear Admiral Jamie Barnett.
A statement issued by Barnett said that the woman stands by her assault accusation.
Barnett said that Sinclair "literally sabotaged her career by altering her orders to keep her under his command and refusing her many requests to be transferred. She was literally trapped and bullied by one of the highest ranking officers in the United States Army."
Michael Biesecker contributed to this report from Raleigh, N.C.
Follow Jeffrey Collins on Twitter at http://twitter.com/JSCollinsAP