I NEED HELP TURNING A GUY DOWN

I've made friends with this one guy in my classes but recently he's been giving sly hints that he might wanna be more than that and I've been nicely brushing it off because I am happily in a relationship, but he just asked me to hang out with him and I need help nicely wording out a response to him saying that I am not interested and I'm in a relationship. Part of me feels bad for possibly leading him on and the other half of my is saying "bitch you owe him nothing that's on him". Any advice?

UPDATE: I told him that I had a boyfriend and that Ide love to hang out as friends. He didn't reply for a while but then said it was okay and now we are just going to be friends! Thanks everyone!!