I think we had a misunderstanding. The friend relationship is unbalenced when the guy wants a FWB/Girlfriend|boyfriend relationship, and the girl wants another girlfriend/platonic-friendship. In the situation the girl knows this to be the case, and continues to entertain the idea.

I'm not suggesting that you're obligated to date/reciprocate or entertain the guy's fantasies. Just let them know whats what and don't encourage that kind of unbalanced relationship. Props if you can pull that off and give feedback about why you wouldn't bang him without giving him an impression that he has a chance or attempting to destroy him.

My suspicion for the last part of that is becoming a wing-girl for him and helping him to see that there are other girls out there.

It's beginning to sound like you are talking about a specific situation where you feel you were wronged, because a girl actively lied to you about what she wanted out of the relationship. That sucks, but you should try not to generalise this to 'women are like x'. And if this has happened more than once, then either you are consistently misreading social situations (feeling led on when the woman has no idea you are thinking that way) and /you/ need to fix that, or you are consistently trying to get into a relationship with terrible people (on the off chance women are actually constantly leading you on), and /you/ need to fix that because what you're dealing with there is not 'women' but 'terrible people'.

I don't have that issue anymore, because I'm better able to tell when a girl is interested or not and when I get the slightest hint of that happening I gtfo of there. I've seen this happen to lots of other friends.