This is the sort of thing which I can imagine not going down too well - through being discussed a ton already or whatever. Still, read this article - http://www.buzzfeed.com/krystieyandoli/why-the-friend-zone-is-actually-dangerous-for-women and thought it was decent.
I really agreed with the vast majority of it, I've known people to act like this and think it's been something reinforced in the past - especially with Hollywood tropes etc. reinforcing this behaviour. I can't begin the account the number of 'romantic' films about some guy hanging around a girl until he finally 'earns' her or whatever.
That said, a couple of things in it seemed like possible assumptions in it (I don't know them or their lives at all so don't know the context). The main thing was Tracy feeling betrayed by that guy 'biding his time, plotting and planning'. It probably was the case, I don't know, but I've had a couple of spontaneous, one-off totally unexpected hook-ups with friends in the past and would hate them to think it was some sort of plan.
TLDR: growing realisation that some men think of sex as something earned and the implications of that are potentially rough.