What does this mean?

Depends on two things.
- How long has he been together with that ex-girlfriend?
- Did he leave her because of the new girl?

1. Longer than 3 months = Yes / Less than 3 months = No
2. If yes = Yes / If no = No

Yes!!!

Pretty much. The guy's probably been playing on the girl and dating that girl he hasn't had much trouble finding. Right?

not nessicarily. one question to ask is how long they've been dateing, if it was a realy long time then thats not a good sign. but realy it all depends on the cercumstances. if you dont kno the details and you havent heard both sides of the story your not in a place to be making any quick judgements.
now, if this happens all the time though and hes like, dateing a new girl every week, then thats a sign he's not a guy you want to consiter a real relationship with.