So Solomon wants to tell us 'a story' that he 'observed through the palace window' and that didn't at all happen to him last night on his way home from the bar and because he's the king.
So, a naive young man, let's call him Sholomon, was walking down the street late at night, totally sober and not at all thinking about getting laid because his 700 wives aren't getting any younger. A young, married woman was standing in the shadows, dressed in her best hooker costume. Now, this young woman is, shall we say, a chav: she's loud, refuses to stay inside, and hangs out on the street corner, hoping to attract men, despite her married status. As Sholomon passes by, she grabs him, kisses him, and says she has something to tell him. Oh, and does he want to see her new bed coverings? Egyptian cotton! 500 thread count! Also, she wants him to check out her new perfume, a combination of myrrh, cinnamon and aloe. At least it isn't vanilla. 15 years on, for the life of me, I still don't understand why women want to smell like a goddamned plate of cookies.
Finally, she gets to her real point: Come, let us take our fill of love until the morning: let us solace ourselves with loves. For the goodman is not at home, he is gone a long journey (v. 18-19). Because she's willing, and Sholomon has a demonstrable weakness of the flesh, he goes, but he regrets it in the morning, saying, Her house is the way to hell, going down to the chambers of death (v. 27). Aw, does the guy with 300 concubines feel used like a tissue?
So now we know how Solomon got at least one of his wives, and if it happens to be rather creepily similar to his own origin story, well, so be it.