Why is my ex hating?

so I broke up with him after he OD at the movie theater on Vicodin, muscle relaxers and Xanax... he had the audacity to call me pathetic so I quit talking to him. 
Since then I've been having fun, going to work, been doing me. I make a comment on Twitter about how much fun I'm having every now and then... Spreading positivity you know? 
he's never had a job,  let alone made any effort to go to school or get one. So last night I posted a comment about me and this male coworker I work with having fun last night, innocent stuff. He posts a remark on his Twitter saying I'm the most useless and insecure person he's known. This guy, I work with him no romantic interest at all.
So I countered that, he's only making me look like the bad guy cause he's guilty for his wrong doings and he's the insecure one.
Is he jealous that I'm actually happy, with a job and not dwelling over him? Is he intimidated?