Exclusive:Jennifer Garner’s Relationship with John Miller Is ‘Fun’ and ‘Easy-Going,’ Source Says: ‘She’s Very Happy’…read more

Jennifer Garner is enjoying her “fun” relationship with John Miller while continuing to co-parent with her ex-husband Ben Affleck amid his recent split from Jennifer Lopez.

A source tells PEOPLE that Garner, 52, spends as much time as possible with Miller when she’s not with her three kids_ Violet, 18, Seraphina, 15, and Samuel, 12 — whom she shares with Affleck.

“She loves [Miller],” a source tells PEOPLE, noting that the pair spent the weekend together as Affleck is caring for the kids.

“They are serious.

He’s also a co-parent and understands her priority,” the source says.

 “Their relationship is fun and easy-going,” the source adds.

“She’s very happy.”

Meanwhile, on Saturday, Sept. 14, Lopez, 55, and Affleck, 52, reunited and went to lunch together with their kids at the Polo Lounge at the Beverly Hills Hotel in Los Angeles, nearly a month after Lopez filed for divorce from the actor, a source told PEOPLE.

Seraphina and Samuel, as well as Lopez’s 16-year-old twins, Emme and Max — whom she shares with ex-husband Marc Anthony — were part of the afternoon outing.

“They all came together for a fun lunch so the kids could hang out,” the source said.

“[Jennifer’s] trying to be friendly with Ben.

They are still moving forward with the divorce though.

They are working out financial details amicably.”

The source added, “A divorce is never easy, but Jennifer doesn’t want to be selfish about it.

The kids always got along and have fun together.

It makes her happy seeing the kids happy together.

Happy kids are her priority.”