Tokyo Toni told the sock designer he needed to grow up during a tense face-to-face as the couple visited Blac's family in Washington DC.
Tokyo tearfully confronted Rob about his unpredictable behaviour and told the reality star he "needs to work on a few things" for the sake of his relationship with her daughter.
"You're dealing with my only child," she said. "She didn't have a father around. She don't need a baby with no father, do you understand me? You can't do what you're doing, you're gonna ruin it."
Rob had been reluctant to make the trip but agreed to do so as Chyna warned it could be "make or break" for their relationship, which began at the beginning of this year.
Speaking on 'Rob & Chyna', Rob admitted: "We are going to D.C. and being around people I don't know and out of my comfort zone.
"But my relationship with Chyna means everything to me so I am willing to do this."