I just took my boards, so I can share my experience in this area. It's probably a good idea to prepare your S.O. for how little time you'll have available when studying, but there are definitely consolations you can make. I'm not an expert in these matters, but here's what worked for my girlfriend and I. As a disclaimer, we live together so this may not apply to all. For one, it's important to get used to doing some studying at home just so you can have face time where you can share jokes/interesting stuff you're learning, etc. Even though you're getting work done, it's not nearly as isolating for them as if you were at the library or a coffee shop.
As for the weekend, I pllanned a night off/week into my schedule and would use it as a date night of sorts for dinner & movie or something similar.
Another thing that worked out well for us is that many of my guy friends were in relationships as well. So on say, friday night, we'd get together and play a trivial pursuit-type game with Underground Clinical Vignettes (yeah, we're total dorks) while the girls went out. It actually worked really well in that the girls didn't have to stay in on friday nights while we guys dorked up the Barnes and Noble or school PBL rooms. Plus, it allows you to see your friends without using your night off for them instead of your S.O.
Oh, and I can elaborate more on the trivial pursuit game if anyone's interested. It was good fun.