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Diddy 's ex-girlfriend is testifying about the pain she says she went through during her relationship with the mogul ... saying she had to fight off multiple infections and other ailments.

"Jane" -- the pseudonym one of Diddy's exes is using on the stand -- has run the court through the many freak-offs she says she participated in ... telling the jury she kept doing them because she loved Diddy and wanted to make him happy. Gallery Launch Gallery Getty

Jane even says she got a nipple piercing for Diddy because she says he told her it would turn him on if she did.

Jane says she went through with the piercings ... but, she explains they ultimately got caught on her lingerie, causing her to bleed and her nipples to become infected. Play video content

She testifies that sh

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