This sounds sooo familiar!! My OH has been going on about the 'other house' for over a year now. It is funny as it varies between knowing this is our house but then almost in the same breath, asking how I managed to buy it (and all the furnishings) without telling him about it. Then asking if I saw the people about who was paying for what etc. Packs his briefcase at night, gets his coat on and then asks me to take him home, back to the other house as he wants to go to bed and that his where it and his clothes are etc. My daughter suggested taking him around the block and then come back and tell him we are home......suppose it might work. He usually accepts that he should go upstairs to bed although occassionally gets annoyed with me when I say this is our house and his room is upstairs and we don't own any other house. We have lived here for 35 years but have extended the house 2x while here, changed the fireplace etal and I think he is finding the 'new' house as opposed to the original house confusing and so thinks the original house is the 'other ' house he thinks we have. I believe although he was diagnosed with Dementia - Alzheimer's, that in fact he has Lewy's Bodies type - on a daily basis he 'sees' people, on the neighbours roof (reading a newspaper!) or in our house, sitting in our lounge etal and/or hearing noises that are not there - very acute hearing especially of sounds no one else hears!
Good to know that at some point he will stop asking about the 'other' house.....patients (mine) wears thin after going over it serveral times every day. You also can't say we will go see it later and hope he will forget as that is exactly the type of conversation he will remember and then say you said there was another house and you were going to take me there. I find distraction is the best option - saying we are going to do somehting or dinner is ready etal as he then usually stops going on about the other house - although usually only a temporary respite and a topic brought up again later in the day.
I have found it comforting that my OH is not the only one doing this!