What should i do? pls someone?

i met this guy maybe 2 months ago. he is from another town so i don't know much about him. i'm friend with his sister buy they are different and i think not so close. so we've met one night and we were talking about casual stuffs. that we've chatted on facebook several time. he had play here in my town and we were smiling at each other. i really toughed he likes me because we never talked once till that night and after that we were talking and chatting and why would someone to that if you don't like the person. anyway on new year i was with his sister in another town for 2 days and when i got home i saw that he is in a relationship. that he wrote to me when are you coming home and happy new year. i said i'm already home and you sister too and we were laughing because he didn't know and told how did he spend the night and stuffs like that. i really like him and now he has girlfriend. i'm felling so down...how to get his attention i don't wanna mess in his relationship but i think i might love him. help!