"Matt is very happy for Ben and J.Lo. They're all close friends and get along well. It's nice for Matt to see Ben be in such a great place in his life and in his relationship," the source shared.
The source added that Affleck's close friends can see how well the actor is doing since he rekindled his romance with Lopez.
"Matt is glad that J.Lo and Ben are back together in this new, more mature way. Ben is doing really well and all of his friends can see that," the source said.
Affleck, Lopez and Damon were spotted in Malibu near Paradise Cove over the weekend, with Affleck and Lopez strolling hand-in-hand while Damon walked alongside them in photos obtained by TMZ. Damon has been a big supporter of the couple rekindling their romance, telling Desus & Mero that nearly two decades later, things are much different for the once-engaged pair.
"I have to say, the press was particularly terrible to them, like, 18 years ago," Damon quipped.
As fans recall, the couple -- dubbed Bennifer -- first started dating in 2002 while starring in their first movie together, Gigli. They quickly got engaged, but in 2003, they called off their wedding just days before their planned September ceremony. They officially split in January 2004.
"What's nice is that at least they're being nice this time around," Damon added on Desus & Mero, before cracking a joke. "They're on vacation right now, but he still responded when I hit him up about the Red Sox yesterday…You still have priorities!"
"J.Lo and Ben's relationship is serious," the source shared with ET.
"They have insane, on another level, chemistry. They are both super passionate and are head over heels with each other, just like they once were," the source added. "This time around, however, they both really feel like this is it."