To tell or not to tell...

Should I warn the new supply? She is actually someone he started talking to after my initial D&D. She lives in another state quite far from here but she came here once on a business trip and I am assuming they already knew one another. Anyway on one of their messages she asked him about past relationships. He said that the last person he dated (me had the personality of nails on a chalk board and that the other lady he was recently attempting to talk to was boring. I guess he couldn't get enough supply from her since she is miles away so he initiate contact with me again which lead to my last D&D but I do know that he would contact her from time to time checking in. I do not know but I believe he may have turned to her. Do I stay out of it? I hate that he goes around treating people like this. I would not wish him on my worst enemy. I amazed that people here at work thinks he is a great guy with a good head on his shoulders. If only they knew his other side.