Questions: Break Up & Divorce

I was dating this guy, but ended things because he didn't know what he wanted. Now, I realized that I still like him very much and still want to be with him, despite his faults. Anyhow, I found out through mutual friends that he is seeing someone. It's not serious afaik, and apparently she is moving too fast for him - she's treating it like a long-term relationship. But he's just going to treat it as something meaningless to him (as told by mutual). I also found out that he did regret losing me, but didn't understand why I ended things. We were together for almost a year, and after I ended things, he got with her soon after, and a lot of people were surprised by that. He also met her on Tinder, so it wasn't like he knew her before. Anyhow, I contacted him recently, just to catch up. Not once did he mention the other girl he was seeing (bad or good sign?). Secondly, he hasn't initiated any texts with me (mostly bad), but responded to all of the texts I sent him. He also hasn't declined any requests to meet up, but he's kind of flakey for example, "I'm pretty busy this weekend, but I might be free blah blah" Our relationship didn't end on bad terms either. But I'm afraid he didn't take this break as serious as I did, and just found another rebound to shut his emotions away. We have plans to meet up soon, but I don't plan on bringing the other girl up at all. Also, it's weird because the girl and I have the same first name.. (like what). And if we do meet, I am going to just play it cool, not going to bring up any relationship stuff or anything serious like that.

TL;DR: Guy I dumped got a rebound girlfriend, can I steal him back?

Anyhow, I miss him, and cherish what we had, so is it possible to start over with him even though he's seeing someone else? Or should I just leave him be with this new girl?