What makes them want to have sex? Finding you physically attractive and then you turning her mind/body towards sex. That's done with your voice, your eyes, and most importantly, your hands and mouth. You have to get her turned on. Being alone doesn't automatically mean sex. If she's not sexually attracted to you in the first place, this just won't happen.
Are they not letting you touch them or kiss them? If this is where you're hung up, then it's a lack of sexual attraction and there's nothing for you to "do".
If they are, and it's not going past this, then your issue is not doing it right. You need to learn how to turn things more sexual as quickly as possible, while keeping her comfortable and enjoying it.
Give me the exact sticking point and I can elaborate further.
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Quote:
Build an emotional connection through your hard throbbing cock.
Build trust and comfort by holding their hands and covertly rubbing your elbows on their nipples.
RSDTyler