"She had a great time with Ben," a source tells PEOPLE of their getaway. "She is happy with him and enjoys spending time with him."
The duo's trip to Montana comes over a week after the exes were pictured outside her Los Angeles home in late April.
Earlier on Monday, sources told PEOPLE they were spotted riding in a car together near a resort in Big Sky, where Affleck, 48, has a home. He was seen behind the wheel with Lopez, 51, in the passenger seat. Photos of their outing were published by The Daily Mail.
"[Jennifer] spent several days with Ben out of town. They have a strong connection. It's all been quick and intense, but Jennifer is happy," a separate source told PEOPLE of the pair who were later spotted arriving back in L.A. on Saturday on a private jet.
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Lopez and Affleck were engaged in 2002 and costarred in the films Jersey Girl and Gigli. They postponed their 2003 wedding days before they were set to walk down the aisle, then officially split by January 2004.
Before being spotted in Montana, Lopez and Affleck both attended and participated in the VAX LIVE: The Concert to Reunite the World event, which aired May 2. (They were not pictured together at the L.A. venue.)
Listen below to the episode of our daily podcast PEOPLE Every Day for more on Jennifer Lopez and Ben Affleck's vacation in Montana.
Last month, Affleck commented on Lopez's glow in an interview with InStyle when the mother of two graced the cover of its May Beauty Issue.
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"Why do you look the same as you did in 2003 and it kind of looks like I'm in my 40s … at best?" he joked as Lopez later told the magazine: "I don't have any [beauty] secrets except JLo Beauty — and I'm giving them all to everyone with every product. Ben is funny! He still looks pretty good too."
News of Affleck and Lopez's outings come after she and ex-fiancé Alex Rodriguez released a joint statement on April 15 announcing the end of their engagement. Multiple sources previously confirmed to PEOPLE that Lopez ultimately broke up with Rodriguez, 45.
Affleck previously dated actress, Ana de Armas. The Deep Water costars split in January after first being romantically linked in early 2020.