A stylist who testified that he witnessed Sean Combs repeatedly beat Casandra Ventura, his longtime girlfriend, and was privy to her discomfort with the sexual encounters at the heart of the mogul’s sex-trafficking and racketeering case came under questioning on Thursday by the defense.

The stylist, Deonte Nash, is a critical witness for the prosecution because he said Ms. Ventura told him several times that she did not want to participate in the sexual encounters with male prostitutes, called “freak-offs,” that prosecutors say Mr. Combs demanded and directed.

Xavier Donaldson, a lawyer for Mr. Combs, began questioning Mr. Nash on Thursday morning about what he knew about infidelity in Mr. Combs and Ms. Ventura’s relationship — a main theme of the defense.

The cross-examination became animated as Mr. Donaldson began inquiring about a flirtation Ms. Ventura had with the actor Michael B. Jordan in 2015 that is said to have spurred Mr. Combs’s jealousy. Mr. Nash cut in: “Yes, I did hook her up with Michael B. Jordan — I know where you’re going with this.”

The defense has argued that Mr. Combs’s violence toward Ms. Ventura was motivated by jealousy and drug use, not issues related to sexual coercion.