How can there be pain in a place where there is so much joy? A loving relationship is the most awesome experience in the world. This is why it also holds the potential for so much sadness.
There are so many things that can go wrong. We must remember, "Better to have loved and lost than not to have loved at all." If we have this attitude we can hold ourselves together during the hard times and rejoice that we have this awesome gift during the good times.