It could be anything: Another girl who's piqued his interest...or he's lost interest in you...or he's too busy to date. But no matter what the cause, the result is still the same- you need to figure out if this suits you.
From where I'm sitting, he's just a guy who you've known a very short time and haven't even met yet. Suggest you don't get yourself too keen on someone you've had very limited exposure to. Cynicism is a good thing to keep in the back of your mind in the very early days.
Keep your mind open to dating others and see where it all ends up.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.