The "Cambia El Paso" singer showed off a rather steamy kiss with the actor while celebrating her 52nd birthday aboard a boat on Saturday.
In the photos posted to Instagram, Lopez wore a red and yellow chevron, two-piece bathing suit, paired with a brightly-colored caftan, gold jewelry, and a sunhat. Meanwhile, Affleck, 48, opted for a casual button-up top on the water.
"5 2 … what it do …💗," she captioned the romantic images.
Saturday's birthday post marks the first time Lopez or Affleck have shared anything about their rekindled romance on their own social media accounts.
A Hollywood insider told PEOPLE in this week's issue that the pair "are madly in love" and "the loves of each other's lives."
For more on Jennifer Lopez and Ben Affleck's trip in St. Tropez and other top stories, listen below to our daily podcast PEOPLE Every Day.
"They want to do everything they can to make this work," added a Lopez source
Lopez and Affleck, 48, originally began dating in July 2002 and got engaged that November before postponing their September 2003 wedding days before the date. They ultimately called off their engagement in January 2004.
They were first spotted spending time together again in April, following her split from Alex Rodriguez.
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Since then, the pair have regularly been spotted hanging out together and spending time with each other's children.
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leah remini/instagram Jennifer Lopez, Ben Affleck and Leah Remini
A source previously told PEOPLE in June that "it's very obvious that Jennifer is serious about Ben."
"Everything seems to be running smoothly," the source added. "She hasn't looked this happy for a long time."
For more about Jennifer Lopez and Ben Affleck, pick up the latest issue of PEOPLE, on newsstands Friday.