<human>: Can you succinctly summarize the text in 1-3 sentences?

So in short, there's a guy in my class who seems to be interested in me.  It's mostly been casual small talk during class, with him asking me what classes I'm taking, where I live on campus, etc.  But the other night he texted me asking if I wanted to go to a party with him.  I responded something along the lines of "I'm actually busy tonight.  Thanks for the invite though!"  I wasn't sure how else to respond.  It's not like I could've been like "Um, sorry, but I have a boyfriend."  Then just last night, we had a group meeting, and he offered to walk me home.  I declined and made up some BS excuse about how I had something to do before I went home.

I'm at a loss, because he is being super casual and hasn't made it explicitly clear that he's interested in dating me or anything.  But, I do feel like if he knew I had a boyfriend, he might not be casually hitting on me the way that he is.  I'm not really attracted to him at all, but he's a nice guy and I think he's not be excessively aggressive or creepy or anything.  Asking to walk me home just seems courteous.

I guess my main question is, should I tell him that I have a boyfriend?  And if so, how?  Should I text him randomly and let him know ("Hey, I just wanted to let you know that I have a boyfriend.  You're a really nice guy and I didn't want you to think that I was just being rude"), or wait until he asks me out again?
<bot>: Guy in class is kinda hitting on me.  How do I let him know I have a boyfriend without being a jerk?