It's all in your mindset. Truly.
WHY did you take the dog? For yourself or for the dog? to help the DOG right?
Ok -- so keep thinking that way. You've taught the dog all you could? Now, if this dog goes on to have it's own family will it have more attention? Willit get more attention? Will it be able to grow emotionally and fulfill it's true needs as a DOG? (to give unconditional love, to bond tightly with it's humans, to be a star in it's own right?)
If you are fostering JUST because you "like dogs" then you really aren't doing it for the dog. If you're doing it for the dog then look at where it can go with this placement.
THEN you can get another.
But when you take on a foster **truly** you have to consider that dog a FOSTER with every single breath you draw. It always ALWAYS has to be the "omega" -- it always has to have a different set of rules than for YOUR dogs.
In my house fosters stay ON the floor 24/7, no bed, no furniture, etc. -- why? Because some homes may not allow it and I don't want the dog to learn at MY house something that it will get in trouble for elsewhere.
In my house MY dogs know a foster ***IS*** temporary -- the different rules enforce that. So the jolt is less when the foster is placed -- it protects MY DOGS as well as the foster. If you treat a foster exactly the same way you treat your own then the foster thinks it's a "failure" and you just bounced it ... again.
It's a subtle difference, but it helps. It helps with the transition and it helps both the dogs and you.