Can men and women just be friends? There's a reason this is such a popular question. I think the obvious answer is "no," and the only people that ask this question are those who are looking for excuses to justify their true feelings towards someone of the opposite sex.
To be friends, a man and a woman would need to share genuine love and care for each other without any feelings of attraction. Love and care happen to be two of the three most important components of a relationship (the third being attraction). It's so easy to fall for a friend when you already have most of the feelings towards that person that you would for a boyfriend or girlfriend. All that's missing is attraction. Attraction, however, is much more important for men than it is for women.
For men, attraction is something they either do or do not feel from the start, and it manifests itself in the desire for sex. Because men’s desire for sex is so strong, it’s not that hard for a man to feel attracted to a number of women. There you have the third most important component of a relationship: attraction. What about the first and the second - love and care? The man grows to love and care for the woman for whom he feels a lot of attraction.
For women, attraction is something that builds over time. It builds much faster when they already have strong feelings of love and care for someone. For example, a woman might meet someone to whom she is immediately attracted, but a relationship will never build from there because she might feel completely incompatible and incapable of loving that person. Attraction is not enough for a woman.
In a situation where a man and a woman are friends, the woman becomes more and more attracted to the man because of her feelings of love and care towards that man. The more her feelings of attraction grow, the more she feels for her friend. At the same time, the man is already feeling a strong desire for sex. The stronger his desire for sex, the more attraction he feels for his friend. Seems likely that the friendship line will be crossed. As long as one of the people has feeling for the other, then it's probably not a true friendship, anyway.
I say go ahead, cross the line, and get it over with. Isn't that what you've been wondering about this whole time anyway?