If a woman has a close friend who is a man, it usually means that he likes her and that's why spends much time with her. She, on the contrary, considers him only as a friend. It's like she says: "You're a nice guy, but I don't want to "do it" with you". It's just the same as if a person came to a job interview and his employer said: "Your CV is wonderful, we've been looking for so competent a person as you, but we can't employ you, unfortunately. However, we'll use your CV as a basis of comparison with other CVs. We're going to employ someone who is more unskilled than you, though. We'd rather he was an alcoholic. And if he didn't work well, we'll employ someone else, but not you. Actually we'll never employ you. But we'll be calling you from time to time and complaining of those we have employed".