Ventura, a rhythm and blues singer known as Cassie, is the star government witness against Combs, who has pleaded not guilty to five felony counts of racketeering conspiracy, sex trafficking and transportation to engage in prostitution.
If convicted on all counts, the 55-year-old rapper and founder of Bad Boy Records would face a minimum 15 years in prison and could face life behind bars.
Ventura has told jurors that Combs coerced and blackmailed her throughout their 11-year relationship, which ended in 2018, into long drug-fuelled sexual performances he called "Freak Offs".
She has testified that she hated Freak Offs but participated because she loved Combs and wanted to make him happy.
Jurors on Thursday were shown text messages from 2009, where Ventura told Combs she was always ready for a Freak Off and was ready for sex.
The defence also showed emails and text messages from early in the relationship, where Ventura and Combs professed love for each other and she sought more attention from him.
"I wanted to spend so much time with him, at this point in 2010, because I'd fallen in love with him and I cared about him very much," Ventura told jurors.
Ventura, married to personal trainer Alex Fine since 2019 and pregnant with her third child, spent a day and half answering questions from a prosecutor.
Combs is being tried in Manhattan federal court.
He has since September been held in a Brooklyn jail when not in court.
A lawyer for Combs said Ventura's cross-examination may take two days.
Defence lawyers have signalled they will ask Ventura about her own alleged history of domestic violence, and whether a desire for money motivated her to get back at Combs.
Part of the criminal case stems from Ventura's November 2023 civil lawsuit against him.
She testified that he agreed after 24 hours to settle for $US20 million ($A31 million).
Asked on Wednesday why she decided to testify against Combs, Ventura said she could no longer bear the emotional burden of years of his physical and emotional abuse.
"I can't carry the shame, the guilt, the way he treated people like they were disposable," she said.
"What's right is right, what's wrong is wrong. I came here to do the right thing."
Also known during his career as Puff Daddy and P Diddy, Combs founded Bad Boy Records and is credited with helping turn artists like Mary J. Blige, Faith Evans, Notorious B.I.G. and Usher into stars in the 1990s and 2000s.
The criminal trial could take up to two months.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
