Hey, these guys (most of them) are escapists, the fact that one of them managed to make it doesn't mean that you are a terrible owner!
This is something that can happen to everybody! Please don't be hard on yourself, instead try to concentrate on the positive facts: he is flighted, that means that he's in a very good position to fend for himself while you look for him. And as Tielfan says, there's plenty of food around.
Either you will find him, or hopefully someone else will, you have no idea how many tiels are found every year! One of my own guys is a rescue who was found nice and placid sitting on a tree in a children school playground, he must have come from very far so the owner was never found.
But now with all the bullettins and internet rescue pages you have a good chance to be reunited even if he has gone quite far from home.
Don't give up hope and be kind with yourself please!!!
