Jothar: We have a saying that you know something is off when couples spend too much time with each other. Shabbos is meant to spend with one’s own family, and one should not get too “close” to someone elses. As Rabbi Weinburger points out, bad things can happen.
oomis1105 (Just as an FYI): The Rema (OC 333) says that Hachnasas Orchim is only when you invite people who are out of town, but just inviting someone over for a meal is not included. There are Nafkei Mina in Halacha, as pointed out there.