E! News has learned that the lovebirds arrived on a private jet to Cabo San Lucas, where they checked into a private beachfront home in a gated community dubbed Casa Oliver.
The mansion costs a cool $9,500 a night and features a private chef, butler, and personal masseuse who is on tap for daily spa treatments.
There's also a private gym located inside the pad, where Jen and Justin have been working out daily to keep their bods in tiptop shape.
According to an eyewitness, the engaged couple has "spent most of their time by the pool, tanning and socializing with friends."
"Jennifer and Justin have been very affectionate, kissing and snuggling up to one another. She loves to sit with her arms around him and lean into him for kisses," the source added.
"They aren't shy about public displays of affection…they can't keep their hands off one another. They seem very happy together and totally in love. They haven't spent a lot of time apart on this trip. Wherever she is, Justin is right next to her."
But it isn't just a couples' trip for the A-lister. Our insider says "Jen has also spent a lot of time with Courteney, working out with her, and swimming in the pool. They seem to be the best friends they have been for years, always chatting and laughing together."