From a legal and not emotional standpoint, what is the criteria for paying monthly payment?

Marriage has crumbled and the spouse(husband) wants to leave, but knows he has some obligations as for as making the monthly payments on the house, he does make the monthly payment by hiself, however, both he and the wife's name are on the deed, title,etc on the house as owners? What, in percentage, is he responsible for if he leaves, which is enevitable?