I need advice, ASAP please?

Chances are high that there is someone else in the picture. EXACT same thing happened to me... We hit it off right away, such good chemistry, he liked me, I liked him, he randomly stopped talking to me, and got a girlfriend haha. You didn't do anything wrong, don't feel like it's your fault... Guys tend to move from girl to girl especially when they are single... It's messed up completely and believe me I know how hard it is to want to give up but you like him so much. ugh it is quite frustrating... But guys will be guys and you have to look at him and think, was he really as good as I thought he was? Plus, he is the only one missing out! You deserve someone better! Good luck, I'm glad that there is someone else who shares my same problem!