This guy I am friendly with said that we should take a vacation together while I'm single. We aren't like best friends or brother and sister close type of relationship. He probably wants to have sex with me then, am I right?
Not necessarily, he might just want to have a good shot at developing something between you two. You spent so much time together when you're on vocation that you get so many opportunities to make a move, and they don't have to be sexual. He definitely wants something out of it whether it be just sex or a relationship, no one really knows except him. If he has always been that "nice guy" then I think he just wants to have a relationship, but just doesn't know any other way to get you interested.
I don't know if he wants casual sex from you or if he wants a relationship, but if he wants to go on vacation just the two of you, I would guess he wants something. And if you don't, I would expect a very expensive, very uncomfortable vacation.
If your friend is a nice-guy, he's definitely looking for more than a friendship and is hoping that this vacation will seal the deal. Every nice-guy makes the mistake of thinking that he can be promoted from friend to boyfriend if he' s a good enough friend. Of course, that doesn't work, but they think that way because it would work for a guy.
Men don't have well-defined, inescapable friend zones. Liking a woman as a friend doesn't make her any less attractive as a girlfriend. In fact, the opposite is true. If she's attractive and has a cool personality why wouldn't I want to give that a shot. Personally, I think our way of thinking makes more sense, but I admit that I'm biased.