You ask a lot of questions about why your crush did something with another girl? It's because he isn't your's. Guys cannot read minds and signals rarely work. Your crush may find you attractive and be willing to date you, but you can't reasonably expect he will ask you over every other girl. If a guy is single and looking he'll have several girls he's considering. If you don't make your feelings painfully obvious he may not choose you regardless of how attractive he thinks you are.