I am terribly allergic to cats. Decades of working in shelters and a boarding kennel has not lessened the reaction in the least. I cannot go to my sister-in-law's house, because she has several cats. I can tell if someone owns a cat by standing beside them for a minute, behind them in line at a store, etc.

I could never live in a house with cats. It's just not physically possible. I am not even sure I could live in a house where cats had formerly lived, without completely replacing the carpet, painting, etc.

I would just go to his house to visit, instead of him coming to yours. As far as moving in together, if his allergies are less severe, some of the above suggestions might work. Maybe the cats could stay in one level of the house, or in certain rooms only?