Yes... who tf else would I be talking about? DO NOT TALK TO HIM ANYMORE. He's your ex and you owe him no explanation whatsoever. Everytime you talk to him you encourage him to say something else to you. Stop encouraging him and do not respond to any form of contact he gives to you. zero.
Save every text, every email, every voice mail and put your phone on record if he comes to you in person so that you have proof that he's harassing you. I suspect he'll stop soon enough if you stop enabling him to do what he's been doing. He's not even your "ex" per se because all you two were was FB's so stop this cycle and quit talking to him altogether.