Long distance relationships generally happen for a reason. One partner may get a job in another city, go back to school, or need some time to take care of family business. All of these things can happen on timetables; all of them can have a firm end date. If there is no time table for reuniting with your significant other, that's a problem. If you don't have a date to look forward to, your will to work through rough spots will diminish. If you have no idea when a tough situation is going to end, it is much harder to justify to yourself why you're putting yourself through it in the first place.