As a shy boy I have to say: force them out of it. Drag them along with you.
If it seems like they're okay with it, they love it. If it doesn't seem like they're not okay with it, they don't like it.
If they're shy, confront them with the questions you have.
At worse, you'll just find out that they don't have an interest in you (unlikely, or why would they have hung out with you that long?) or that they just aren't ready and/or are too immature for commitment. (most likely)
Personally, I've never hung out with a girl I didn't like. ...but I've never dated either. :(