Certified GKH Gardening Expert
Though there are some dwarf varieties of Weeping Cherry that can grow to 8 feet in height, most Weeping Cherry trees can grow quite large, even as high as 40 feet. For this reason growing in a pot would not be recommended. I believe your tree is stressed due to being pot bound.
Hopefully you have a spot to plant this showy tree in your yard.
I have listed a few links for you with more information about proper planting and growing care.