Wow...he's been through an awful lot.
Well to help gets his bowels normalized you can add 1 teaspoon of canned pumpkin or 1 teaspoon of plain yogurt to some wet food. Also another remedy for diarrhea and to stabilize intestinal health is to cook some oatmeal in water. Many cats enjoy the oatmeal and the yogurt plain, but you can mix it in his wet food.
If you feel that he has dehydrated from the diarrhea you can give him some unflavored Pedialyte, 2 droppers every 1/2 hour for 2 hours. This will to get his system hydrated and it generally makes them feel a bit better.
When you say traumatized, is he showing other symptoms?
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