How do i show a guy i dont like him without bein a jerk?

k so there is this guy that i dont like but evreyone thinks i like cuz we hang out alot but i dont and i think he likes me he ALWAYS flirts with me and his cheeks turn red and he touches me whenever he can (not wrong but he has a gf and she is my friend how do i show the guy that i dont like him without bein a jerk?