Jimmy,
This site advocates sleeping with a girl on the first date - is that any different? So is every girl just using me for sex? (not a terrible thing) But what if I want more of a relationship? If I'm never supposed to take it slow, but taking it fast disables any dating options, where does that leave things?
Every girl
wants sex when she's going home with you on the first date, but not every girl is
using you for sex. In one sense, you don't really have any control over whether or not a girl decides to see you again. However, there are things you can do to greatly increase the chances that she
does want to see you again. Obviously the quality of the sex is very important -- if she's not leaving your bedroom with her head spinning after multiple orgasms, then she's probably not going to be too inclined to stick around very long.
The next thing that matters is how you treat her after sex. Are you still warm towards her? Do you become at all suddenly needy (or too aloof) after sex? Your post-coital tone needs to feel the same as it was during the date when you were building up sexual tension toward your night. Usually when I'm finished having sex with a new girl, there's a period where I'm just lying there naked with her with one arm around her having a few laughs and maybe sharing a few interesting things about myself (as a reward for allowing me to sleep with her). After sex, she has to feel like there are more layers to you to uncover, and that she's only just learned enough about you to keep her interested.
After the girl leaves, it's also important to send her the post-sex text: "Hey Jane, I had a great time last night. Hope you did too

" ...or something along those lines. This should be sent sometime during the middle of the next day as to keep her from getting in her head too much about how you feel about the whole interaction with her went down (i.e. she might be thinking "did I sleep with him too fast? does he like me? did he use me for sex?"). Assuming the entire interaction went well, she'll usually respond with something positive.
If you want to see the girl again, then this next part is important:
you should contact her again within the next 3-5 days to arrange your next meet-up. If you do it too soon, it sounds a bit too needy, and she'll wonder if she accidentally slept with a guy who is super clingy. However, if you wait too long, you risk sending her into auto-rejection by making her feel like it was just a one-night stand (which is fine if that's all you want). But what you don't want to do is make her feel like it was a one-night stand by taking over a week to contact her, and THEN contacting her to see her again -- that's going to make her feel like you're just using
her for sex. You can arrange for the meet-up to be the following week if you want to, but you need to contact her
before a full week has passed.
When you do get in touch with her again, you want to invite her directly over to your place. If you suddenly decide to take her on a "date," that's actually going
backwards in her mind, and it will only confuse her. So make sure to be very casual about it and say you'll cook dinner together (or whatever it is that you want to do). You pretty much rinse and repeat this process for several weeks; if she continues coming back, then she's obviously hoping she can turn it into something more.
Of course, you'll want to make sure that you're only seeing these girls again if you want to keep them around for a longer period of time. If a casual or long-term relationship is not something that you're looking for at the moment (which it sounds like you may not be, but that's up to you), then you can pretty much send her the post-sex text and leave it at that.
- Franco