How to let a guy down easy?

well this guy was over my neighbor's house and he's kinda a flirt so i went with it we kissed made out a little but he's 2 years younger than me i feel i might be kinda awkward when school started me in 10th him in 8th also i still am very attached with my old crush we don't really speak but that's cause it's hard to see each other and well honestly to him i'm a friend bu i can't forge him and i feel like there's something there so how can i let this other guy down or can i sill hang with him like when he was at my neighbor's house?