Given the fact that there is scant evidence, successful recovery is a long shot and even if you are successful in obtaining decree in your favour, by that time you would have spent equal, if not more, amount than you lent to your Cousin. And even then you will have a mere decree in your hands, virtually in the same position you are in ie. to recover the amount. To implement Decree you have to follow procedure through Court which involves more time and again expenditure.
Instead, take the assistance and involvement of family elders and strike a settlement where he admits all the debt, including interest and payment schedule and get it signed by your Cousin and elders duly getting it notarized. This time, if he fails, you will have very strong ground for legal action.