What is his problem?

Hi all. I was with guy for about almost 6 months a year ago, I didn’t do anything wrong at all , long story short he made it a thing to get with my BFF and he did ! “My bff” and him started to date afterwards and that “BFF “ is no longer a bff by the way. Anywho year later I’m living my best life, work and personal life I’ve been doing so many things great things for myself not giving a care in the world about these individuals espcially him. I found a fantastic man , I have a great new job , life is good I can say ! :) I’m minding my business that the point LOL. This immature idiot of ex everywhere I go at work he walks away if I’m there , if he seems I’m in a certain area he avoids it , I’m there he walks away unfortunately we work in the same place. He wasn’t doing that before now he’s doing it again and makes it so obvious! He’s been taking down on me too badly with coworkers and upper management I don't know why. I smile , I laugh and show no care in the world just why act this why honestly? Lol
What is his problem?
Post Opinion