While I didn’t read the comic and not sure if DC has it in the library, here’s what I think happen since I made this up. Let’s see how close I am to being right…
Hal Jordan was in a bad mood one day, and the Guardians wanted to talk to them, when talking turns to arguing, the Guardians took Hal’s ring away, and sent him back to earth. Meanwhile the Guardians had the green ring choose someone to replace Hal, and the ring chose Kyle Raynor! When Hal heard about the new Green Lantern he became so furious and with Jealous and hate, he became Parallax and becoming a main villain for the new Green Lantern. Kyle tries to make peace with Hal, but when Hal won’t listen, they became a enemies.
I did see that years later, Hal became a good guy once again. Thankyou DC for bringing him back as the Green Lantern. 