Ben Affleck and Jennifer Lopez Kiss Outside His Home

Ben Affleck and Jennifer Lopez reunited after spending his birthday weekend apart, and it clearly felt so good ... they couldn't keep their hands off each other.

Ben and Jen shared a long, passionate kiss goodbye at his home in Brentwood Tuesday after spending the day together ... and it looked like she attempted a quick grab at his booty too.

As you know ... it's usually the other way around.

Either way, Bennifer 2.0 appears to still be going very strong following his 49th birthday ... which Ben celebrated with his kids instead of J Lo. She was also seen later in the day with her son.

Another interesting note -- J Lo had someone with her as she kissed Ben goodbye, and the woman was holding a script for Lopez's upcoming action thriller called "The Mother."