My question involves collection proceedings in the State of: New York

My uncle signed on as a co-borrower for my first year of college. Since then, my mother and grandparents made the payments on time until I graduated. Then I took over. I always pay it, but rarely on time. I'm a graduate student now and having an especially hard time being on time with payments, but I always make them. The most I have been behind is nearly 60 days, but I have never defaulted on it (default is 90 days). My late payments are effecting my uncle's credit and he is now threatening to sue me (and my mother, who is not on the loan) if I continue to make late payments.

Can he do this? And what would be the likely outcome? I know as a co-borrower he's legally liable to make payments on the loan if I cannot, however he has only done this on one occasion, after I had suffered an injury several months ago and could not work. Also, I don't think my mother has any liability, since she is not listed as a co-borrower. I really do try, in earnest, to make this payment every month. What do you think?