The singer Casandra “Cassie” Ventura, a former girlfriend of Sean “Diddy” Combs and central character in the case against him, took the stand on Tuesday as the high-profile federal trial of Combs enters its second day in lower Manhattan.

She is expected to testify against her former partner for several days.

Testifying while eight and a half months pregnant, Ventura was initially asked to describe her relationship with Combs: “There were violent arguments that would usually result in some sort of physical abuse. Dragging, different things of that nature.”

Early in her testimony, Ventura was asked to describe Combs’s “freak-offs”.

“It basically entails the hiring of an escort and setting up this experience so that I could perform for Sean,” she said, adding that it allowed Combs “to watch me with the other person and actually direct us on what we were doing. Eventually it became a job for me, pretty much.”

Ventura emphasized that she felt a “responsibility” to make Combs happy.

“I was confused, nervous, but also loved him very much,” she said, later adding that he “controlled a lot of my life” and used many of the videos he took of her during these “freak-offs” as “blackmail materials”.

She then recalled her first meeting with Combs, in 2005, when she was 19.

“I just knew that he was this larger-than-life entrepreneur, musician. Was a fan of the music. I didn’t know too much about him personally,” she said, adding that she went on to sign a 10-album deal with Combs’s record label.

Ventura later released her debut album in 2006, but it would be the only one she ever put out on Combs’s label.

Of how her relationship with Combs developed, Ventura explained how he kissed her on her 21st birthday and that the incident made her uncomfortable. From there, despite their 17-year age gap, they began to see each other more frequently and “started to develop a comfortable relationship with each other”.

She then explained how he gave her oral sex and then pressured her into reciprocating.

“He made me feel crazy for not reciprocating, at the time I did not understand that kind of relationship and I was in a relationship with someone else,” she said. “I was just so young and did not have the vocabulary for some of the things we talked about. I was just trying to understand it, just completely inexperienced at that point.”

After the pair started dating, which Ventura said “was not public for many years” as Combs was still in a relationship with long-time partner Kim Porter, Ventura described the world Combs lived in as “much different” than her own.

“He had assistants at his beck and call. He could get anything done quickly. He had respect from everyone and he traveled quite a bit,” she said.

Ventura depicted Combs’ tempestuous moods and the resulting violence he’d inflict on her if she didn’t act a certain way. She said she never knew if he would show up at her home in Los Angeles happy or yelling, prompting her to have constant “stomach-in-knots” moments.

“Make the wrong face and the next thing I knew I would get hit in the face,” she said. “He would say, ‘Watch your mouth.’”

Combs, who was arrested last September, faces charges including racketeering conspiracy, sex trafficking and transportation to engage in prostitution. He has pleaded not guilty and denied all allegations.

Wearing a light-colored sweater, Combs hugged some of his lawyers and greeted family members upon entering court on Tuesday.

Daniel Philip, the second witness called on Monday and a former manager of a “male revue show”, was back on the stand on Tuesday morning after not finishing his testimony on Monday.

In his earlier testimony, Philip said that at some point in 2012, Ventura paid him to have sex with her in front of Combs, and that similar encounters took place multiple times over the following year or so.

During more than an hour of graphic testimony, Phillip said he once witnessed Combs throw a liquor bottle at Ventura and, on another occasion, drag her by the hair into a bedroom. He testified that he then heard what sounded like slapping and her screaming coming from the bedroom.

On Tuesday, Combs’s lawyer Xavier Donaldson asked Philip if Casandra Ventura “was in complete control of everything she did” with Combs.

“I cannot say that,” Phillip said.

Phillip later testified about Ventura’s drug use and noted its infrequency during their encounters. He also revealed that he had bigger feelings for her: “Had she ever given me the chance to date her, I absolutely would have.”

On Monday, a jury of eight men and four women heard opening statements, and testimony from the first two witnesses called to the stand by the government.

Prosecutors allege that Combs ran a “criminal enterprise” through his business empire, aided by associates and employees, that engaged in crimes such as sex trafficking, kidnapping, arson, bribery, enticement to engage in prostitution and obstruction of justice – allegedly dating back to at least 2004.

In opening remarks, prosecutors accused Combs of using threats, violence and coercion to force women into sex acts with male escorts at drug-fueled parties that he orchestrated – events known as “freak-offs”.

Combs’s defense attorneys acknowledged that Combs perpetrated domestic violence in the past, but denied any involvement in sex trafficking or a racketeering conspiracy, and portrayed any group sex as consensual, describing it as part of a “swinger’s lifestyle”.

Following opening statements, the prosecution called two witnesses on Monday, including Phillip and Los Angeles police officer, Israel Florez, who was working as a security guard at the InterContinental hotel in March 2016 when Combs was caught on surveillance video assaulting his then girlfriend, Ventura.

Combs’s family, including his mother, Janice Combs, and his children, were seated in the courtroom’s front row on Monday. During Phillip’s testimony, Combs’s three teenage daughters left the room.

In accordance with federal court rules, the trial is not being televised. If convicted, Combs, who has been jailed since his arrest last year, could spend the rest of his life in prison.

• Information and support for anyone affected by rape or sexual abuse issues is available from the following organizations. In the US, Rainn offers support on 800-656-4673. In the UK, Rape Crisis offers support on 0808 500 2222. In Australia, support is available at 1800Respect (1800 737 732). Other international helplines can be found at ibiblio.org/rcip/internl.html