Scared of being intimate

So I'm 18 I have had sex before but there's this one guy, we have been friend for five years now and id say we are pretty close, earlier this year he told me he thought he liked me you know more then friends:/ I obviously told him no because it would ruin everything:// but recently we have been hanging out more and it's been so nice, on the drive home he goes what would you do if o said o still liked you......I was shocked I just replied I do t know but now two days laters he's all I think about.....I feel like I wanna be with him but too scared to do it, all I think about is sex and how could I be intimate with him but in reality that's all I want to do....I'm stuck please what do you think i should do???