You shouldn't feel stressed or upset for even one minute. While it is a shame that the girls are being separated they are hopefully going to good homes where they will be loved and cared for, and that is directly related to you taking the initiative to help these girls in the first place. They may have seemed bonded, but honestly, they really aren't that old that starting out with new people to love them separately. Being an only dog (if they will be) can mean lots of spoiling and attention that may not be possible in some homes with multiple dogs (you are an exception, of course). You should still feel great that you have helped these little girls on their way to a new and exciting life. Too bad we won't get to see them grow up though.
Bookmarks