Following Kylie Jenner's 21st birthday celebration [1] last week, Khloé Kardashian and Kendall Jenner escaped to Puerto Vallarta, Mexico, for some sun and R&R with their boyfriends, Tristan Thompson [2] and Ben Simmons. On Sunday, the couples were spotted lying out by the pool and working on their tans. Khloé sported a black one-piece and shared some PDA with Tristan, while Kendall opted for a sexy blue thong bikini [3] and went jet skiing with Ben.

Kendall has been quietly dating the NBA player [4] since July, and even though she has yet to officially confirm their romance, People reports that she's "very protective" over it [5]. "She's being very private about her relationship with Ben," a source told the outlet. "Kendall's really different from her sisters in that sense. She honestly doesn't want people talking about who she's dating and is very protective of her personal life. She hates the attention. She's having a good time with him. She's excited to spend the Summer with Ben."

Khloé and Tristan, on the other hand, welcomed their first child together, daughter True [6], in April and are clearly committed to making things work [7] following his cheating scandal.