What are my obligations if about 5 years ago, I took a Sallie Mae student loan for IT school which my girlfriend at the time co-signed for?
Based upon what you have written about you are legally responsible for reimbursing your "ex" for the loan she co-sogned for and paid off on your behalf. Given what you have written about the right thing for you would make arrangements with your "ex" to begin paying her back whatever you can afford on a monthly basis.