Generally, I consider a partner someone that you do business with, while a boyfriend/girlfriend/spouse is someone that you're fucking. Of course, you can always go into business with your fuck friend, and you can always fuck your business partner (literally or figuratively), but that's neither here nor there. To me, calling your  boyfriend/girlfriend/spouse a "partner" adds an unnecessary air of pretentiousness to the whole thing. It's kind of like calling a comic book a "graphic novel," or referring to every movie you see as a "film." It's not wrong or anything, but it tends to make a person sound huffy.