Good evening, and I'm so sorry to hear of your troubles. Unfortunately, after you recovered from your issues and you had this discussion, you should have both executed a Health Care Proxy, which is a very simple document that says "if I am unable to make my own medical decisions, I want THIS PERSON to make those decisions for me." The forms are readily available at hospitals, and even at Staples, and all it takes is a signature and a notary. Perhaps your fiance executed one and didn't mention it- look around your house.
If you can't produce anything like this, you need to get to an attorney quickly and have him/her file an application to make you the guardian for your fiance. If you've had a relatively long term, stable relationship, coupled with your fiance's lack of readily present family and the lack of relationship he has with his grandfather, I'd say you have a pretty good shot at it. But really, in the absence of a Health Care Proxy, this is the only way.
If you can't afford an attorney, look here: http://www.valegalaid.org/. They offer very low cost, or sometimes free legal services for Virginians. If have some money, but don't know a lawyer, look here for a referral from the bar: http://www.vsb.org/vlrs/.
I hope this was helpful. If you have questions, please respond. If not, kindly rate my service to close this thread. While you may have paid JustAnswer, the experts are not paid until service has been rated.