it's disagreeable, but I don't think you can do much about him. He hasn't DONE anything to you. ! Don't worry for the moment. Just keep your distance. He seems to take the hint, no, judging from your conversation.
"(M)I only see you as a friend and it's disrespectful to pursue somone that is happily in a relationship"
Normal people don't talk like this. What the hells wrong with you?
Anyway, no, you're not being stalked, and people will do this a lot. It happens, it's called being pervy, if you want. It's weird, slightly invasive and uncomfortable but you'll come across it plenty, it's usually if not always harmless, I wouldn't worry. You need to be firmer than 'I love my boyfriend', though, when it gets to that point. That's flabby. You need to tell the guy to f*** off, at least.
*smh* He's not stalking you... Stop being a "crazy"... Just tell him you are not interested in him, and tell him to stop calling you. Then ad him to your block list if you don't want to hear from him... Texting someone 3 time sin a half hour doesn't equate to stalking... Get over yourself.