The reality star, 34 — who has been dating the 19-year-old since last September — posted a photo on Instagram, Saturday, of the model dressed in a black bikini and sunglasses, posing on a rocky shoreline.
“Water,” Disick captioned the shot of Richie, with the ocean visible in the background.
A source told PEOPLE in November they are “very serious” and that the daughter of Lionel Richie has been a positive influence on Disick, who is a father of three with ex Kourtney Kardashian, and has openly struggled with alcohol abuse.
“She’s been great for him,” the source said. “She’s made a big impact on his life and hasn’t partied at all since they met.”