Sounds like the perfect situation I agree with all that's been said, and it is true dogs do live in the moment and don't have the emotions which we have, I know how hard it is though I went through a rehoming of my border terrier, and it was the hardest thing I have ever done, I relinqished her to the border terrier rescue I kept her until they had found her a home, and I felt so bad I pleaded to have her back and was inconsolable but it was the right thing for her at that time. I did think I would never get over it, but I did she is doing well in her new home, and along came Archie and for all his challenges is my lovely little man and has helped me enormously.
Sometimes the hardest thing but the right thing is to do what is right for your situation and mostly as you have done what is right for the dog or dogs in your case. Im sure he will always remember and have a special place in his heart for you as you have for him, but it's lovely that he has settled in so well.
The main thing now is to move forward and enjoy the fact that you can still visit him and have a happier situation.
Well done.