I know he likes me but i keep chickening out???

My guy friend likes me and i've liked him for a long time now...so when he asks me to go make out wih under the stairs i always make an excuss why i can't...now i think he's losing interest...i need help, i cant lose this guy...I need ways to flirt with him and stuff...he's a few years older than me but i'm in one of his cles...he's the best guy ever and he's in a band...plz help...how to i get him to realize that i really like him without looking desperate and how do i get him to want to go out with me and to go out with me...we're both single...but i need to do this before he finds someone else...PLLLZZZ help...any advice would be nice