There are many tricks I can share with both my female and male clients on how to get 'The One'.
In addition, and being very direct here, when it comes to guys: if they have sex with you, if they see you on a regular basis and if they introduce you to their friends, as far as they are concerned, the issue is closed. And if they did not bring up the subject of 'let's be boyfriend and girlfriend' that means just that.
They are dating; they are not necessarily your boyfriend, because that means commitment. And of course, there is the dreaded stage of rejection.
Once there is a commitment, who knows what's next, marriage? Yes, even when considering asking "Would you be my girlfriend? It's not uncommon for a guy to suggest to his girl to become something more than just a girl in his life only to get laughter in response.
Perhaps she was trying to be cool, yet it somewhat backfired given the sensitive male ego that comes with the territory.
The best way to approach the situation is to be straight forward. Do you really like the guy or are you more 'lets see where it takes us'?