He's sure a cutie. I know how easy it is to love your fosters, but just think about how many more dogs like him that you can help if you let him go to a different home where he will be loved and cherished. If you keep him, you probably won't be able to foster any more dogs like him that deserve a chance. Of course, if you decide to keep him he'll have a great home.
Personally, I would just want to meet the family and ask that they send updates, but I would let him get adopted because I would want to keep helping more. The first is the hardest, but it won't be easy to give any of them up. My last foster would have been perfect for our family (and we were looking for a dog), but I had already had a few people email about her within a few days, and I had committed to bringing her to the event. She got adopted by a family that week that loved her and as hard as it was for me to give her up, now we have Boo, who couldn't have been a better choice.
I know you'll make the best decision, good luck with whatever you decide to do.
-GoingNowhere