Ask Mr. Smarty Plants

It sounds like transplant shock, from your description. Even if a tree will go perfectly in a site, it is still going to need some coddling for the first few weeks or months it is in the ground. I hope you have a hose that reaches that far; otherwise, you're going to be hauling buckets of water. A newly planted tree needs water slowly dripped into the new soil until water appears on the surface. This needs to be done every other day, especially since we are getting into the hot season very quickly.

When we probed a little more, we found that although there are 54 members of the Salix genus that are natives to North America, the weeping willow, or salix x sepulcralis, is not one of them. It is a hybrid of the Chinese Peking Willow and European white willow. This USDA Forest Service website has some more information on the weeping willow, including the fact that it is considered invasive in several states, and they don't show it growing at all in Texas. But what do they know? The same site says that the tree is susceptible to several diseases and insect damage, so, hopefully, your tree didn't come with that. We also found an ad for a "Texas weeping willow" which may be what you have, but it didn't give the Latin name for the tree, so we have no idea what that is. Here is a page of images of salix x sepulcralis.

Since the Lady Bird Johnson Wildflower Center is dedicated to the planting, protection and propagation of plants native to North America, we don't have any information on this tree in our Native Plant Database. Hopefully, watering as we recommended will perk your tree up. If you suspect it is something else, we suggest you go immediately back to the nursery that sold it to you and ask questions. If the tree was already diseased when you bought it, we would think you should get your money back.