I think it is a bit over the top to be keeping where he lives a secret. i think it's safe to agree with saffie and say that he's being immature. but not sure if it's worth bringing it up with him.
you could say that it may be necessary to know where he lives in case there is an emergency (mobiles get lost or flat and not possible to reach him or vice versa). and that d shouldn't be asked to keep secrets. but i don't think this is a conversation for now. maybe in a month or two when hopefully you care less about it, but just bring it up mainly so he knows that you know that he's asking d to keep secrets and that it's not appropriate.
but will that help that he knows you know about keeping secrets? will he change his behaviour? i guess that's what you need to answer before bothering to bring this up.
