Thats not necessarily true. I slept with someone on the first night (only wanted sex, wasnt looking for a relationship) and we went on to be together for the best part of a year. Im not reccommending always sleeping with someone on the first night, but its not always true that if you do, that's all you get.
But with that said, I agree with most of the guys on here... whenever a guy tells me how much he likes me... thinks im beatiful etc I always assume they just want sex then if it happens, it happens on my terms because I know whats going on.
Do what sookie6 said, tell him where you are in this- if he wants you like he says he does, hell tell you- he might want to take it slow, but hell tell you. If he doesnt, its a lesson learnt and hopefully you would have picked up a few tricks you can use on guys! :P