Australiian citizen owed money by US citizen

[Liberty Moon]

I am Australian, and was in a relationship with a US citizen, I paid some of his debts of which he asked me to do and said he would repay this was in July of 2001 I have since ended the relationship and he is now putting off paying my money, while he doenst dispute owing me money, just says I will get it when he is ready to pay. He lives in the state of Florida, I have sent him a letter asking him for an expected date for payment or a payment plan to repay the money, he had agreed to pay interest on the money he owed, but its getting the money. The amount he owes me is approx $12,500 AUD + the interest. How can I go about colecting my money, do I have to do this from Australia or because I was in Florida when I lent him the money, and the fact that he is a citizen there, do I need to take action in Florida.
Would very much appreciate some information as to what to do here. Thankyou very much