I'm biased, as I work with my spouse, but this is I think an overblown concern. People leave companies for all sorts of reasons, many of them dumb. They do not need to have made a lifelong personal commitment to their manager to find those reasons. Also, people do not need to have made that commitment in order to access their unprofessional self; normal team members find ways to be deeply unprofessional without entangling their relationships into their companies.

Yes. Strictly speaking, if you get into business with your significant other, you are increasing the cardinality of the set of things that can go wrong with your team. For people that think like us, maybe that's where you stop thinking, and if so, fine. But the set we're talking about is very large, and I also know high school statistics, and so can observe that the relationship stuff is unlikely to be the event that blows up your team.

Believe in working with your spouse (or close friends, or whatever) or not. Either way: it has nothing to do with negotiating for a job, and it's a little creepy to bring it up here.