Responses
The manga your looking for is most likely Kuroneko Kareshi no Asobikata. They're partners, though.
could it be this one
http://www.mangago.me/read-manga/mimi_paradise/
im looking for that one two but i cnt remember ;^;
Long time ago I read a yaoi manga with black cat (uke) that was in a box in the rain (I don't remember) and the next thing I remember that there was a white cat/dog (don't remember; -;) and they become friends/family. The white one is the seme and he's the older. Sorry for bad English *~*