Maybe ask him outright who he loves, or even likes, more. You or some dog ? Depending on his answer, you may be able to find a non-confrontational way of suggesting that, in that case, he should stop bringing the subject up, feeling hard done by, and put it behind him.
Besides if it is his dream of having a dog ought he not be accepting all responsibility for it ? It's not your dream, after all.
Maybe this should have been sorted prior to forming a permanent relationship, but that's in the past and you need to solve the issues which are in the present.