What should I do? And how would I tell him no?

So my friend asked me to come with her to this boy's house tomorrow night, she's been talking to him forever and they've been planning to hook up for so long and tomorrow is finally there night, she told me one of his friends is gonna be there and he wants to hook up with me. I want to, he's cute and he seems really nice I've never met him before though. I've had a little bit of a ... promiscuous past.. I'm 16, I still have my "v card" and all but I've done everything else and a lot of people know that about me. I don't want him to expect that I'm going to do more with him just because I've done that stuff before. I don't want to, I'm not like that anymore. But I don't really know how to say no to someone.. And it sucks because I want him to like me too. But what if I have to say no? What should I do?