It's not too late. He signed a written contract with the landlord to be responsible for the lease and then he left. He also had an oral contract with you to pay for half of the rent (plus utilities, and other things too?). In FL you have 4 years to sue on an oral contract. He breached when he stopped paying you his half. Figure out how much he owes you and sue him in Small Claims court.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.