I'm sorry to say he is sick, and you will need to get him to a vet as soon as you can.
In the meanwhile, do you have a medicine dropper? How about some liquid vitamins for birds? If not, go to the pet store and get a bottle of them that has the dropper. Usually they say you can put it in the water, or if a keet is having health issues, you can administer it directly to the bird. If I were you I'd give him 2 drops of liquid vitamins.
In addition to the vitamins, see if you can get him to eat some broccoli or dark leafy greens. This will give him additional vitamins, and nutrition that he needs.
Water is also very important, especially if he's having diarreah. You can either wash out the dropper you use for vitamins, or wash your hands well, dip a finger in water, and give it to your keet from your finger. This way you know he's getting some water in his over heated, dehydrated system.
Hopefully this will help him a bit; however, you REALLY need to get him to a vet ASAP tomorrow!
Good luck sweetie!