Luyendyk confirmed widespread speculation that the couple were seeing each other in October, just weeks after Robertson ended her engagement to Ben Flajnik.
Speaking to Life & Style, Robertson declared that she is very happy with Luyendyk.
"Yes, I'm dating Arie," she told the magazine, adding: "We're enjoying our time together."
Robertson also praised Luyendyk for treating her better than Flajnik did following their engagement on the season finale of The Bachelor in March.
"I was miserable with Ben; he treated me so badly," she claimed.
She added of Luyendyk: "I didn't want to jump from one public relationship to another, but Arie and I get along, and I'm not going to let that get away."
Luyendyk finished second on the most recent Bachelorette season, with Emily Maynard ultimately choosing Jef Holm as the winner.