EX why does He do this to Her?

If an ex acts like he doesn't care about you, but can't keep himself from talking about you to other people?? Negative or Positive, there's always something. One of my colleagues separated from her boyfriend a little over a year ago, and whenever I see him or any of the people I know see him, he usually mentions her. He also uses her to boost his confidence, by saying false comments about her not being over him when she hasn't ever talked to him, called or given him any reason to believe that. I doubt it's out of bitterness, because when it comes to their past relationship, he was the one that confidently ended it. When she's around he acts cordial, nice and normal. Behind her back, completely different. He always brags about being so happy with himself and his life, but if that's so, why would he feel the need to say it so much? I know you can never know for sure, but what could be possible explanations for his behavior??