Since today is Leo Tolstoy's birthday , my recommendation to you is to read "Anna Karenina" - it covers your issue in full. In the novel, there is a brief reference to how proposing to a high society maiden is different from visiting a prostitute because... a high society maiden can turn you down / reject you whereas a prostitute cannot. According to my part-time boyfriend, this is no longer the case - apparently modern prostitutes can refuse a client, at least in Amsterdam (no, he does not visit them because prostitutes do not turn him on, but he appears to be in the know). I do not know where you yourself live and whether the prostitutes in your area are as protected as those in Amsterdam - Amsterdam is, after all, a civilized city that offers protection to sex workers, but regardless - you still get the crux of the issue - in the world of non-paid sex (using the term with which you titled the thread, but more generally, in the world of any relating not mediating by monetary exchanges), you are exposed to the risk of being rejected, hurt, abandoned, dis-preferred, and so on and so forth. Not everyone is prepared to take this risk...

Read the novel - this point is minor, so the script of the recent movie with Keira Knightley omitted it. I have not watched earlier film versions - I suspect they omitted it as well, as a minor point. But it fully addresses your issue (with word economy that was not, in general characteristic of Tolstoy's writing), so read it!