Debts Owed by Business Associate are in My Name

Over a year ago, I allowed a business associate to use my account with one of my suppliers in order to purchase stock for his business over a period of 3-4 months. The payment terms of the account with the supplier was 7 days. The associate would order stock and pay me. I was also ordering stock from this supplier during this time and was benefiting by allowing the associate to order using my account. Towards the end of the above arrangement. Over a period of approximately 3 weeks the associate ordered around $4000 worth of stock, most of which i was not aware of. There were several orders placed that added up to $4000, none of which were paid. After this I did not allow him any further use of the account due to this not being paid. The associate acknowledges that he is responsible for this debt, the supplier is also aware that the associate is responsible for this debt and the accounts department of the supplier has regularly called him asking for payment. The supplier is now forwar