He really needs to see a vet. Any time that a pet cannot eat or drink normally, your vet may need to intervene and help to provide food to him that his body can process. Sometimes this involves bypassing the esophagus by passing a tube to his stomach and administering food there. It would be wise to find out what is causing the "loose esophagus" and finding out if there is a treatment. Sometimes if there is something irritating or injuring the esophagus, giving it a break by passing an NG (nasogastric) tube can help the esophagus to heal and may give him the ability to eat normally again. I know of a few human medications that have been tried in animals for like situations, some with and some without success. A main concern with a pet that cannot swallow properly is aspiration of food or drink which can lead to pneumonia. Please have him seen by your vet as soon as possible.
Also to note, prolonged periods without normal food consumption for a pet (resulting in weightloss) can put undue stress on internal organs and can cause internal problems.
Good luck!