My bfs house has black mold

So I do not often go to my boyfriends house due to certain issues but I did one day go over to his house and I discovered black mold on the walls. I mentioned the black mold to my boyfriend and he basically glossed it over but he didn’t say how his ceiling was falling apart in one room in his house from the overgrowth if black mold and he didn’t even seem to care. Now his house is quite run down but it has me thinking of my future I want to marry him but when the adults in his house die and he gets the house what do we do? Is the house completely unsellable? Can I fix it up? I think the black mold spread all around his house it would take a fortune to fix the house but the black mold is something I don’t know what to do with. Someone please give me advice on what to do because I’m the only one thinking about it