Bella Thorne Reunites With Ex-BF Gregg Sulkin Post-Scott Disick

Bella Thorne is treating her PTSD -- post-traumatic Scott Disick -- with a dose of her ex-bf, Gregg Sulkin ... just in time for his birthday.

Bella and Gregg did lunch and a movie together Monday. The exes grabbed burgers in Studio City before taking in the flick for his birthday celebration. They broke up last summer, but Bella was still clinging to him as they strolled.

She also hung out with Gregg at his crib. And by hung out ... we mean lying on his back while wearing just a bra.

Bella seems to be screaming "Scott who?" Of course, he's moving on too.