Should I not talk to him anymore?

I say stop talking to him too. He could just be trying to get from you - or he could genuinely care. Either way, you deserve to more than a 'secret' friend. Just tell him it bothers you that you feel like he's hiding that he knows you. Dont be mean about it. Let him decide if he wants to come clean about your friendship if it actually means something to him, or if he cares more about fitting in. Also, don't take offense if he chooses to fit in. High school is tough and some people aren't strong enough to stand up for themselves (he might be one of those people).