I am really not into this guy and my friends are starting to annoy me...what do I do?

This guy who works on our college campus apparantly likes me. He's asked me out several times, and I keep saying I'm busy. After giving me his number and asking me to contact him several times, my friend said that i could text him from her phone just to be nice, that way he doesn't have my number and she can block him later. So we did that. Except, he keeps texting. So I told him I'm in a relationship and am not interested. Yet he still texts. So I don't know what the deal is. Now to add to this annoyance, my friend whose phone we are used to send him that one text, she keeps giving me crap for not texting him back. Saying how its rude and I'm being a jerk. I don't know this guy, I'm not interested, and only texted to be courteous and make it clear I am in a relationship and not interested. What do I do about this all? He texted again tonight, and I told her not to reply. She didn't, but she said she felt bad for him and I'm being rude. I told her I owe him nothing, and I don't want to reply. Am I doing the right thing here?