Why hasn't he asked me out?

Okay, here's the story. Im 17 and he's 18, just to start.
We go to school together, but we started talking online a lot about a few weeks ago, shortly after me and my boyfriend broke up - which he was fully aware of, as he actually works with my ex.
Now, almost every day he still starts a conversation with me online, and he is somewhat flirty, and always joking a lot. I get the impression he likes me, but the odd time he does see me in person, like in the one class we have together, he doesn't go out of his way to get near me, even as we're walking out.
I think he's pretty shy, and he does seem kind of nervous the few times we have talked in person. I can't imagine that he just really likes to talk me online constantly, if he wasn't looking for something more. We have a lot in common, and I've tried to be flirty too, but he still hasnt even mentioned wanting to date me, or liking me. He's knows Im single, and I know for sure he is too.
Some reasons I've considered are:
- Because he works with my ex, he is hesitant to date me (theyre not close tho)
- He's really shy and just doesn't know anything about this stuff
- He's thinks it would be taboo to not wait longer after Ive just gotten out of a relationship
- He likes the thought of being with me, but when it comes right down to it he doesnt want a girlfriend
- He wants to wait and talk for a while longer before taking any steps
- He doesnt realise I like him and is afraid of getting rejected
Any other reasons anyone has are appreciated!!
I'm really at a loss here, but I have really good intuitions, and they're saying he likes me. I just don't know why he hasnt asked me out. Advice anyone?

ps: I know some ppl might say, why dont you ask him out? But I really cant do it, then I'd just have the added worry that he'd only say yes out of obligation or whatever, and I just dont need to worry about that too.
Also, we dont have any common friends, so I cant really get any of them to find out, haha.