As a start-up he simply may need to get approval to add the job you've discussed at this point in the companies life cycle. If he's wrestling with something like that, he may not disclose it and your communication must be strategic to avoid driving him away.
As a CEO you need to assume he has the balls to tell you if he isn't interested.
As a CEO of a start-up he should also have alot of stuff going on. He hasn't told you you're out....so you may not be #1 (dating another to it's conclusion?) or you are and he has to work through something (could be as simple as his timeframe is not as urgent as yours...happens too often).