What I've learned is never assume that your date is really interested in you on the first date...
One of the more puzzling, disappointing and frustrating dating experiences for men is having women who seem to be interested in them disappear suddenly and unexpectedly. You go out with a girl on a date, who seems to really like you and you even make plans to do things the next time you see each other, and then oops -- she doesn't return your texts or calls. It's hard for a male mind to understand what could possible drive this type of inconsistent behavior.
Among all possible reasons for this behavior, including being on a rebound, talking to a number of other guys, etc., the most common reason reason women disappear after acting interested is this -- they are not really interested in you in a first place. You might be saying – wait, but she was really into me on a date. But, just because the girl acted interested, doesn’t mean that she genuinely intended to get to know you. It’s very likely that she acts interested in every guy she meets, because she is playing the "numbers game" and she believes that coming across as excited and interested is the right way to act with every guy she meets, who she might be interested in, but who is not necessarily interested in now. In other words, acting interest is the proper, polite and strategically right to be "just in case".
More at: Why Women Disappear After Acting Very Interested.