There exists as follows:
1. the possibility of him not having any feelings for you like that.
In whichc ase, he probably want to be friends, or he probably wants to wait and see if he is ready for a relationship. Perhaps he has some past issue, and is probably not ready for anything serious yet, so is just waiting to see how things go before he actually takes a risk. In which case, you will have to accept it, and be his friend, and see what happens, if anything.
2. the possibility of him too shy to ask you out.
Some guys just cant ask a girl to go out like that. He may seem friendly, and flirty, but the next big step he probably has not ever arrived to, or probably unsure how to drive on that road. And also, this point links to the next point.
3. he just being unaware how you feel about him.
He would be worried about you not returning the same feelings, and as a result prefers to let time take tick away and see what develops.
You however seem to like him, and by holding yourself back from asking him, you guys could probably end up developing a relationship that sticks at friendship. So in such a circumstance, you need to ask him out. Of course, if you want to test him, instead of asking him out, suggest it to him. Perhaps one day when you guys meet, when you're leaving you can be like "Hey i am free on *give the time and day*, so maybe we can go out?."
That would be you throwing the ball into his court, so whichever one of the options above it is, he will understand that you're interested to some sort (either as a friend or something more).
Hope that helps. Let me know how it goes