4. You're a Liar.
It usually goes something like this: you meet a guy who is cute and likes you, but he's not really available for a relationship. He has some condition that absolutely precludes his availability, like he's married, or he gets around town on a skateboard. Or maybe he just comes right out and says something cryptic and open to interpretation like, "I'm not really available for a relationship right now."
You know if you tell him the truth -- that you're ready for marriage -- he will stop calling. Usually that day. And you don't want that. So you just tell him how perfect this is because you only want to have sex for fun! You love having fun sex! And you don't want to get in a relationship at all! You swear!
About ten minutes later, the oxytocin kicks in. You start wanting more. But you don't tell him that. That's your secret -- just between you and 22,000 of your closest girlfriends. Instead, you hang around, having sex with him, waiting for him to figure out that he can't live without you. I have news: he will never "figure" this out. He already knows he can live without you just fine. And so do you. Or you wouldn't be lying to him in the first place.