Jennifer Lopez & Casper Smart -- Back Together!

Jennifer Lopez and Casper Smart were back together Monday ... and when she spotted the photog she ducked for cover -- which totally means they're banging!

We think it's JLo's car ... it's definitely not his, although he's driving.

JLo and Casper broke up in June after dating 2 1/2 years. There were reports Smart cheated on JLo with a transsexual, but he denied it and threatened to sue.

As we reported ... the breakup was amicable and they parted as friends. Now it appears there may be benefits to the friendship.