Most Helpful Guy
Well, guys generally process emotional turmoil fater than women.
Additionally, just because he is exchanging numbers doesn't mean he has replaced the relationship you two had.
Finally, if you broke up with him, you should be overly concerned with his romantic intrests anyways.
Most Helpful Girl
He probably just wants to enjoy the newness of a romantic connection again.
My older brother used to do that all the time before he found his current girlfriend. I think it's just because he enjoys the refreshed feeling of a new romantic experience/a clean slate of attraction. I also think it has something to do with patching up any "confidence leaks" after a long term relationship where some things may have been said or done that made him (or other guys) feel bad about themselves. A man's ego can be a very fragile, delicate thing and if it is cracked then they will often seek to repair it with the tits of another woman. Some guys just like the attention; it makes them feel hot and wanted. Don't sweat it. Legit connections typically don't happen so easily. The odds are that it's just romance games and nothing serious.