it was somewhere on this page http://www.asstr.org/~Kristen/beast/ i dont know the name, but i remember what it was about "so a husband and wife are doing whatnot, and the husband starts to try something kinky, with his wifes permission, they start to treat her as a dog. after some time she is slowly turned into a "dog" although she thinks its just for a kinky thing. as time goes on and she is essentially a dog, the husband reveals that he already had a wife, and that their plan was to find someone, turn them into a dog, then get together." it was something along those lines. if anyone could find it i would be very grateful thanks
Source: reddit.com/r/Erotica/comments/1n2gjg/could_someone_help_me_find_a_story