my friend is currently in a LDR, and I actually spoke to her about this the other day.
what I remember is that the two of you have to want to make this work, and it's perfectly normal to have those down days when you blurt out that you think this isn't working- you just have to be open, and talk about your situation sometimes. if someone brings up any problems, they're not trying to break up with you, but to genuinely make it work you need to fix the problems that will arise from being in different places.