"It is like they never broke up, but everything is way better this time," the source says of 49-year-old Affleck and 52-year-old Lopez. "They are all over each other and their friends joke around about it with them."
As the holidays approach, the two are already making plans.
"They plan on spending the holidays together and also taking some solo trips," the source says. "They want to be together all of the time, so their next big things are Thanksgiving and Christmas. There is a lot to coordinate, so they are figuring it out."
Of course, their kids remain a priority. Affleck shares three children with his ex-wife, Jennifer Garner -- 15-year-old Violet, 12-year-old Seraphina and 9-year-old Samuel -- while Lopez shares her 13-year-old twins, Emme and Max, with ex-husband Marc Anthony.
As for how Garner feels about her ex-husband's romance with Lopez, our source says the 49-year-old actress is nothing but happy for Affleck.
"Her kids love J.Lo and J.Lo loves them too. It is all positive," the source says. "When Ben is happy and the kids are happy, Jen feels like there is nothing she can be upset about. Jen also says Ben looks better than ever. She and Ben are getting along so well in a co-parenting sense and all is good."
"It's been fun for them to do activities as a blended family and the kids are enjoying getting to know each other better," the source said. "Jen and Ben are both hands-on parents and their kids are their number one priority, so it's important for them to do things as a unit that make their families happy."
Another source previously told ET that the pair was definitely ready to take their relationship to the next level and move in together very soon, and that their families hanging out together "feels very natural to everyone."
"Their goal is to be one big happy family. They both feel like this was really meant to be," the source said. "Jen and Ben are all about their kids and they are having so much fun together as a big family. Everyone is getting along great and things are really working out for them on so many levels."