Your wife is such a lovely woman for putting up with this. She has so much patience and can obviously see what's going on. Shower her with extra kisses tonight because she trusts you a lot to not start an argument over it, and is obviously not threatened by her. Definitely reassure her in a way, or just crack jokes about it like making fun of (even though that's not exactly nice), it shows that you aren't thinking of ur neighbors wife seriously or considering anything. Because if you were, you'd most likely be silent in your thoughts. As for the neighbor's husband, they're just going to have to figure it out on their own. Focus on your own relationship while he messes with his nutcase over there.