Two reasons: 1) He explained it in front of their coworkers while she was able to hear this conversation taking place, effectively insulting her without risking being called out on his dick attitude (since their relationship was private in the first place); it's a pretty cowardly and dickish way of revealing your thoughts about a significant other; 2) He didn't bother explaining his problems or concerns with OP on a one-on-one basis, which may have helped her with her alleged neediness (if that were the case) or, possibly, the relationship altogether. Considering that at least one of them was adamant about keeping this relationship private (or because relationships with coworkers at the office are strictly taboo), it sounds like that break-up was just a convenient and risk-free way for him to go dip his proverbial finger in another pot.

that's childish..

Wow what an ass.

Maybe he was talking about a different ex from before he dated you? It's a possibility... If he was definitely referring to you, that is incredibly rude and petty of him, and at least you know that you're well shot of such a mean-spirited person!