Although many women and men manage to form and sustain long-term friendships, romantic feelings can and often do develop. Studies show that men are more likely to become attracted to a female friend. This attraction can develop even if the female is in a romantic relationship with another person.
More about being “just friends”:
Many people regard attraction in a friendship as negative and burdensome. People who are already involved in romantic partnerships often find that their attraction to friends can reduce their satisfaction with their current partners.
Men in opposite-sex relationships are more likely to overestimate how attractive they are to their friends. Women are more likely to underestimate their attractiveness to male friends.
Middle-aged people report less attraction to their friends than younger people do.