The simple statistic is that over 90% end if they don't decide to eliminate the distance after 1 year, and actually do it before the two year mark.
There are lots of other factors, but those the basic statistics.
I know a couple who's relationship is going strong at 20 years. The conditions though are that they both like the time apart as well as together. All vacations and virtually all holidays are spent together. My personal observation is that they enjoy their 'alone' time far too much to give up on it entirely.
As for the majority, the first statistic is true and considered so since usually one or both want to 'be' together every day. Monogamy is far easier to deal with unless both have jobs that often require 18 hour days (or for some other reason, they want or need to be available for their work 24/7.) If both truly want an open relationship, living together is a little less important, but it does create the stability of a stable place to rest your head.
Of course there are also those relationships where they are really just FBs and the time together is more of a biological need than emotional attachment.
The central point is honesty and balance. I know it's been said by the other above me, but HONESTY HONESTY HONESTY!!! Remember that.
If you can move, or he can move and the difficulty of moving is outweighed by the relationship, then the choice, while difficult, is fairly obvious (again, assuming there's honest communication.)
When my partner and I met here on RJ, we spent weeks together before the move. I was in CT and he was in Phoenix. I wouldn't move to Phoenix because I was far too accustomed to an environment where I could be out (since I had been for over 20 years) and you can get fired from a job in AZ for being gay. Deal breaker for me. He could move to CT (which he offered) or we could both move to SF Bay area, (ideal work wise for me, and he grew up here so there was a home ground familiarity for him.) Win-win.