H.B.
Even though there is no timeframe in the decree related to the sale, I would imagine that you could file a Motion for Contempt based on the fact that he is refusing to follow the current Order, no matter if there was a set time or not. The judge will likely either force a sale, force him to pay you for his half (if he wants to stay) - and for him to take care of the taxes since you have been keeping them up too!
On the other hand, if your income is now different than what it was when your support was calculated, you may want to file for a modification. You could work up a support revision to present as well as presenting the issue related to the property....
I would get an attorney....I could recommend someone depending where you are located.