I agree - 3 dates is waaay too soon. I think having a rule for everyone doesn't really work.
TheDuchy is right - if someone isn't looking for a real relationship they'll dump you sooner or later no matter what.
Also I don't think it's possible to ruin a potential relationship where you have good chemistry & get on well by not having sex (esp if you are at least having some physical contact). If you think it ended because you didn't have sex soon enough, I'd be inclined to think it was because a. he was only really after sex and moved on when he didn't get it fast enough or b. there was not enough chemistry & compatibility there to keep it going anyway.
I've waited up to 3 months in my more successful relationships (for sex, not sexual contact).
I'd advise taking it slowly and waiting a while, however he really must not get the impression that you're doing that due to a rule or tactic.
If he pushes or expects; just say "I really fancy you, but I don't feel comfortable having sex with someone unless I know them very well, it's just the way I am/have always been" etc. (while doing your best to keep a straight face obviously).
If he dumps or fades, likely he was only after sex anyway.
The reasons for this to me are that; people don't tend to value what they get easily. Also that men (though there are exceptions of course) are natural hunters/sportsmen (hence their obsession with sports, racing, movie warfare etc.) and they are wired to strive & compete to 'win' and achieve things they want... give them reason to feel they have put some effort in and achieved something by getting intimacy( and feelings) from you.
Also, like it or not, many men tend to be v judgemental of women's sexual behaviour, whether they are honestl about that outside of male company or not.
They think "if she did this this quickly/easily with me, she'd do it with every man"; and they get turned off both by the ease/lack of value, and by their primitive "she could cheat easily and have me raising another man's child" thinking.