updated 08/18/2014 AT 10:00 AM ET
•originally published 08/18/2014 AT 11:45 AM ET
Sunning and sparring – that pretty much sums up Nick and Olivia Culpo’s weekend (but it’s not what you may think).
Despite rumors to the contrary, Jonas and his onetime queen of the universe are still as together as ever. The 21-year-old singer and his 2012 Miss Universe girlfriend were spotted in Las Vegas over the weekend celebrating the 25th birthday of Nick’s older brother, Joe.
And it was a happy birthday, indeed – at least judging by the photo of Joe receiving a very, uh, special dance from Little Spinner, billed as the world’s smallest stripper, and a Miley Cyrus performer at the ever-lively Beacher’s Madhouse show on Friday. They also marked the milestone that night at MGM Grand’s Crush restaurant.
The festivities continued into the weekend at the Wynn Las Vegas, where Joe and 17 of his closest friends basked in the sun at Encore Beach Club on Saturday.
“Nick and Olivia walked into the pool hand in hand, and from the way they acted, it seemed like they were as comfortable as ever,” a source tells PEOPLE. “They weren’t overly showy, but they definitely seemed happy.”
The couple of more than a year hung out inside their upper-level VIP bungalow, coming together several times to catch some rays. Toward the end of the day, Magic Mike star Alex Pettyfer showed up. The younger Jonas, the source says, introduced Culpo as his girlfriend.
“Nick was smoking a cigar and drinking a Coors Light while he rested his hand on her leg, the source says. “They gave each other a few pecks throughout the day, too.”
Following the day at the pool, the cute couple opted for something more combative: the debut of Big Knockout Boxing at Mandalay Bay. Sitting near Adrian Grenier and Pretty Little Liars star Ashley Benson, Jonas and Culpo stole a few kisses while watching men hurl wild punches at each other in a small, circular pit.
Jonas knows a thing or two about getting hit: He stars in the upcoming DirecTV drama Kingdom, playing a young, talented martial arts fighter.
Later in the night night, the group hit up XS Nightclub, where the birthday boy was presented with a four-tier cake and champagne.
“Nick was the life of the party,” says an onlooker, “dancing on the couch and making sure his brother was having a great time before breaking away to demonstrate his affection for Olivia, sneaking kisses and sweet exchanges in between photo ops with friends.”