Mortgages and loans will never go out of fashion. Therefore, to build long-term value for yourself, you need steadily growing and consistent traffic. Unfortunately, very few affiliate programs pay for repeat borrowers, so you may only earn the first time they take a loan.
Building a subscriber base and email list is a solid strategy that will allow you to regularly send out new loan offers and build long-term value. You could look at sending a monthly newsletter with some interesting stories, and then include some offers.