The glider is on a very poor diet and may have parasites and/or a bacterial infection. He needs to see a vet as soon as you can.
Tonight, make him a scrambled egg - no oil or seasonings. He really needs some protein. He also needs vegetables and fruit. Do you have any frozen veggies? If not, you can go to the store and buy a bag of mixed veggies that has green beans, carrots, peas and corn. Also, frozen or fresh fruit is good. Nothing canned and nothing with sugar, garlic, onion or salt.