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Cassie wants to see Diddy pay bigtime for his crimes ... and she's letting the judge in the case know she's permanently scarred by the mogul's threats, physical abuse, and horrifying sex acts that led her to thoughts of suicide.

Diddy's ex-girlfriend of 11 years typed a letter to Judge Arun Subramanian ahead of Diddy's sentencing Friday after his conviction on 2 counts of the Mann Act -- which is transporting a person or persons across state lines for the purposes of prostitution. Getty

Cassie wrote she felt trapped in her 11-year relationship with Diddy because he used threats and substances to control her and her career as a singer.

She said Diddy "groomed her into performing repeated sex acts with hired male sex workers during multi-day "freak-offs," which occurred on

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