You are on his credit file as being financially associated and, sometimes, the 'bad credit' of one associate can taint the others standing.
From Experian: "Your financial associates can impact your ability to get credit. Companies view information on your credit report when you apply for credit, such as a mortgage or loan. ... Your financial associates appear on your report, and companies may check their credit history when deciding whether to approve you."
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk