Does your friend have tits and a vagina?
Do you have a penis?
Are you fucking your friend?
Are you gay?
If you answered yes to the first two questions and no to the second two, then the answer to the OP's question would be YES.
One of my best friend's is a woman. She is married and I have no interest in having a romantic relationship with her...doesn't mean I don't think about what it would be like to get her in bed now and then.