How to start dating this guy?

Simple: ASK! Okay, You might be nervous to ask but it'll be better to know now than to have to wait and waste your time. By the way, If he was taken, I don't think he'd be walking you home! ;) Just ask him, 'So I was just wonering if you got a girlfriend?' and if he says yes, say 'Oh I was just curious' and pretend like it doesn't bother you. If he says no, Then ask for his number and hint off that you are interested! Good Luck!