I would start by asking the guy what happened. Listen to what he says, and how he says it.
In fact the how may be more important. If he can’t give you an honest response I think you should walk (run) away. I mean if someone is going to dodge and weave in the first moment you meet him you don’t want to be married to him. On the other hand If he says that “She was a nice girl but we realized that we just would not work” then I don’t see a problem. Its a lot easier to break off an engagement then get divorced a few years later, and if there are children even more so.
I was engaged to someone before I married my wife, and she was married before.