Long distance relationships are a beautifully idealistic phenomena. they can be maintained, (as i agree with everyone else) as long as both parties are on one accord. The advantage that you have when your relationship BECOMES long distance, is that you were blessed with the time to work on the foundation of your relationship face to face. You have a much greater chance of success if your relationship is based on mutual respect and love, -something that you cultivate in a controlled environment, i.e., each others' presence. The only variables in a relationship are the humans. Everything else is background noise. If you focus on your mate and they on you, then you'll be fine, -as long as you're determined to make things work.
BEFORE all else fails, pray about it.
It is very hard if you are touchy-feely and your longing for companionship becomes stronger than your desire for that other person. Thats when the breakdowns occur, where the idea of cheating enters your mind, and where your frustration about the situation rears its head. This can then be passed along in conversation, -where the phone calls happen less frequently and the "I miss you's" are few and far between. Then doubt enters your mind and you begin to wonder if they might be feeling someone else because it would make it easier to depart if its not your fault. Your mind can do some pretty amazing things, including self-sabotage. As long as your significant other remains on the horizon of determination, then the distractions of possibilities elsewhere and the strain of keeping things together will be dramatically reduced/done away with altogether.
My two sense.