I don't understand the whole loan thing, but when it comes right down to it, if the loan is in both your father's and your X's names, it's between the two of them. He can sue her, doesn't make you look any better or worse. Just someone who wants their money. Don't get involved if you don't have to. Simply tell your father if he wants his money, he's going to have to do something himself and you will not be a go-between. However, if your name is on it, that's a different story and you need to decide how to handle that tactfully.
Me: 26 Ex: 27 Son: 5
Divorced: 3/2010 Each day is another opportunity to do it right.