Why does he want ME to ask HIM out?

Okay so like it has been almost 4 months since I really started talking to this guy. He’s told me that in the beginning he was just looking to mess with me but even now I have my doubts sometimes. He is always reassuring me though that he really does want to have a relationship with me. We’ve hung out a couple of times and have been all over each that people have asked us if we are dating. We both tell our friends that we are taken. Especially when it comes to when other people seem interested in us. But we aren’t going out which is the problem. I have no issue with it really because although we aren’t like ‘officially’ going out we still act like we are. But he wants me to ask him out. My sister says he is probably afraid of commitment but that really doesn’t make any sense to me. My friend said he is probably just afraid of rejection, but I don’t know. It seems logical but I’m not sure. I’m wondering if I should ask him out? And why does he want me to ask him out?