Relationship woes?

recently i have met this guy that i thoti could be serious with. but it ended less then a month and i start find out he dirty secrets. he as a one year plus girl with him and his gf had call me and confront me and told me that i'm the 4th girl in their one year plus relationship. He was so conviencing letting me to choose him out of the rest of the guys.he acted so well while blancing me and her at the same time. i thot he was so serious abt me. wen i found out my heart was angry but now the second day of the whole thing my hearts starts to ach. I mean like i have no position to do that then wad abt his gf? i believe that she more hurt than i. but i feel so sad. what should i do ?