Lou
Really don't know what to say - you both must be devastated
My sister is in the same position as you, 50/50 ownership with the Housing Association in a flat, only she has a greyhound and has not told the Housing Association about this (she too is not allowed animals). A few other people in the flats also own animals.
If I were you I would get Bosco back and just keep quiet - but I'm like that, a little rebellious. Trouble is it's whether you're neighbours would keep quiet too. OMG I really feel for you.
Give your little boy a hug from me, I can't imagine how he's feeling xxx