Cazza it might depend on how its worded, I cant remember whether you have an order for your marital finances? If it just says he will pay the debt off then he might not have done anything wrong by setting up a payment arrangement. He might perhaps have struggled financially to meet the payment each month, I think you kept the house didnt you so he would have had the expense of moving and such.
There is no excuse for not giving the loan compnay his address but he must have now resolved that or he wouldnt have been able to set up a payment arrangement.
I''d file a notice with all three credit agencies briefly outlining the circs and then this will be taken into account next time you apply for credit.