Well, I think Sookma is right - the real issue here is trust. This is a little different to a real internet relationship, ie you're not worried that he's really a 12 year old kid or a guy with a wife and three kids
But you are trusting that he is being sincere with you and not just playing with your feelings.
There are a few points that I want to make. First most people aren't out to get their kicks by tricking and humiliating people. I know there are a lot of losers out there, and you do have to be careful, but the majority of people aren't, so it's usually best to give people the benefit of the doubt, and he hasn't really done anything overt that might make you think he is not on the level as far as I can see, though I know that it can be very hard to allow yourself to be vulnerable.
Second it is not at all unusual for shy people to crack jokes - it is actually quite characteristic as it is a way they can be social and fun while still keeping themselves separate from the situation - they can hide behind humour so as not to reveal themselves. Actually humour is used this way for a lot of cases, hiding grief or vulnerabilities is another. I know this, as I am very shy, and I'm told quite hilarious
So as I see it, you have to decide whether you want to trust him, and how much. Of course, the balance is that however much you hold back from trusting him, you are keeping that much of yourself from him. And also what will be the consequences of holding back - you may save yourself from embarrassment and pain, but you may also lose what could be a meaningful relationship. So I guess you have to consider what is more important and what you might lose if he does turn out not to be sincere, and only you know that answer to that.