please help

He left me about 9 week's ago and it felt like I was dying. I was trying to get on with things when he started texting again only little things and stupidly I replied because it feels like I'm obsessed with him. Anyway he said he still loved me and I must admit I fell for it but told him it was unfair to do that to me. He kept asking if I'd met someone else which I haven't and said he hadn't either. Anyway last week whilst we were texting I stupidly looked on his facebook and saw he was in a relationship. My world ended again. So in a text I asked him about it and he denied it said he was single. I didn't believe it so kept asking and he kept denying so when he rang me on Sunday I demanded the truth. He said he had dated her for a week and she was a psycho so he had made a new facebook account. Stupidly believed him until later that night my friend text me and said that she had changed her profile pic to him and her. So I called him and confronted him till he admitted. He has been with her about 5week's. I said I couldn't be in contact and felt guilty that I was texting him when he had a girlfriend which is ssomething I hated when we were together and his ex's were always texting. I wished him luck and he said she'll do for now. Why would he lie to me? Why was he texting me? I feel like my head is not my own anymore and I'm going crazy. I keep crying my heart is racing. Can't sleep or eat. How do I get over this? Hes 32 with a son he refuses to see because he annoys him and this new girl is 21. Please help me xx