Urgent help, please. How do I stop this vicious cycle?

[Chloe Bee]

In a nutshell, I've been dating my colleague on and off, his choice not mine since I'm in love with him. Basically one minute he wants me, and he's all smiles with me and the next he avoids me and is cold with me. At first he was ready for a relationship with me and somehow along the road he changed his mind saying he doesn't want to get attached. Also, as I can see from his facebook timeline, he's clearly dating other girls. He even admitted one day that what he does to me is really bad, and he knows suffer from depression (he thinks that's because I'm a weak person), yet he does these things to me. All in all, I know that this is not going anywhere, so I try to erase him from my life, but I keep on blaming myself and I'm so horrified by his attitude towards me that I have been throwing up (I've never had bulimia before), and avoiding to go to work altogether so as not to see him. I don't know how to stop this and I would really really like advice from people who've been through something similar, please, I'm at the end of the rope ...