When my oldest weaned around 13 months, she just stopped asking to nurse. We were down to one feeding after I picked her up at day care, and she simply didn't ask one afternoon or ever again. I don't think she would have refused, but simply lost interest. My 16 month old is still nursing 1-2 times per day. She was not very demanding at 11 months, but is now!!
I personally think it wold be unusual for a baby to not want to nurse at that young an age without some other reason. I bet he is in pain - have you tried Tylenol 15-20 minutes before feeding him? Maybe try that and change the routine - if you normally feedhim in the rocking chair in the dark, start feeding him downstairs with the lights on. Get him out of that pattern of refusal.
If you want to continue, then I would see a lactation consultant for some advice on how to keep your supply up with a pumping schedule or how to change positions in a way that might make him nurse more.
You said you are his main source of fluid. That is another reason why I think it is unlikely he is just done. Babies are smart - he knows he needs to drink. At any rate, I think you need ot try to nurse or pump until he takes to a cup and you can be assured he is getting milk (protein, calcium, vitamin D).
Good luck. He may be starting to wean, but it is hard to imagine he would go cold turkey. You've done great going this long. I found it personally very sad when my dfirst stopped, so don't feel bad about trying to have a little control over the timing of when you wean... it can be very emotional.