Please don't blame yourself for what happened to King Julien II. You were doing the right thing – giving him the chance to help rear his pups and giving Dobby the chance to have help raising them. If he was not neutered, he would never be able to be with Dobby or any of his daughters ever again.
It should not have ended like this – a tragic outcome that you had no control of and no one could have foreseen. My heart goes out to you.