How can I pay him back/get him to leave me alone?

I have been in quite a lot of debt for a long time and a couple of months ago a man that I knew through one of my friends offered to lend me the money and said I could pay him back whenever so I did. I have been paying him back when I can in small installments but a few days ago he came round to my flat demanding the whole sum of money. When I told him that I couldn't pay it all at once he became violent. He pinned me against the wall and knocked over my lamp and smashed some of my picture frames. He then told me that if I didn't pay him all of the money by next month he will make sure that I pay for it some other way. I have always been able to handle guys like this in the past but it is different now that I owe him money and I'm scared about what he might do if I can't pay up. I would never have accepted the money if I knew it would be like this and I can't go to the police as I think it would make the situation much worse when he found out I had told them. What should I do? Are there any quick ways to make a lot of money?