I am worried i will never be happy. can you help?

i am seriously infatuated with someone and i am worried that i will never be able to get her out of my head. i know its never going to happen between us but for some reason i cant get her out of my mind. im worried that whenever i might meet another girl that this other girl i am infatuated with will pop back in my head. im only 19 and i am struggling to find someone to help me. this infatuation i have is ruining my life and my relationship with my family. i need help and youtr answers will be appreciated. thx every1 xx