I understand that this is a complex situation a lot of people deal with, but I often have to wonder about time management issues in relationships that aren't long distance. I also wonder about the amount of time these significant others need... I mean, sheesh.
I went through pre-med while working ft, granted I'm married and we do live together, but I only saw my husband once or twice a week for almost 2 years (I don't count the time that 1 or both of us happened to be sleeping), and I was usually not in that great of a mood when we were awake at the same time.
I think people in this type of situation need to:
1) Reevaluate the amount of time they need to study... If it's eating you up this much in ug, unless your major is engineering with a side of quantum physics med school is going to be a nightmare of epic proportions.
2) Reevaluate the amount of time your SO wants to spend with you. Are they clingy? Must they see you every day for X amount of hours or else they will call you 50xs a day just to make sure you didn't forget their name and favorite toothpaste flavor?
3) If 1 & 2 don't help, decide what is more important, school or that person.
Good luck