If someone buys you a drink and chats with you, they may simply be being social that night. It doesn't mean that they want to have a close friendship or relationship with you. The fact that he didn't ask for your number should have been enough of a clue that he wasn't interested.
And I agree that you have to make an effort if you're to find a boyfriend. Do you give all guys a chance - or are you fussy? Do you smile at guys if they make eye contact with you?
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.