My advice (from a fellow Domer...)
My girlfriend and I both went to med school at schools about an hour apart. At the time we both thought we were destined for each other and we were going to be the couple that bucks the trend, since every single person says "It's so hard to keep a relationship like that..." We were both busy, so we thought that we were both in the same boat and things would work out. You can draw the parallel between any demanding or busy job.
Guess what, they were right.
It was virtually impossible to coordinate our schedules. We both had totally separate social groups, and what little time we did have to spend with each other was at the expense of actually making relationships with the people you went to school with. Pretty soon we were both miserable because we never saw each other, neither of us had any friends at med school, and were left trying to make it through the grind of the first two years with extreme emotional stress and eventually, pretty crushing heartbreak. It's not fun, and unless you're a completely cold, uncaring, emotionless void of a person, it WILL affect your studies.
I realize this is a bleak picture, and probably sound bitter. But my advice is that beginning medical school is beginning a totally new life. Pretty much everything you had or did before will most likely no longer fit into this new life. You'll have new friends, new relationships, and most importantly, a new career. I personally feel that in order to get the most out of med school and make it the best experience possible, one needs to begin the journey totally free and able to follow it where it takes you. Being held back by anything else, whether it be a significant other, family issues, or other life stuff will be to your education's detriment, and ultimately, your career.