How does one breathe again?

It's been a while since i last sat down and wrote for this blog. it's probably because i just realized that writing about things that upset, or things that delight, is easy. but when something totally unexpected and tragic happens, it becomes very difficult to write, or to find words to express the self.
why do some relationships fall apart? why do some don't? what does it take to hold on to one's partner in life these days? i have friends who are perfectly happy with their married lives. but those who are close to me---truly close friends and other special people around me---have suffered the pain of rejection and separation from people they have planned to spend the rest of their lives with.
again i go back to that line in the movie Under the Tuscan Sun: when someone tells you he/she doesn't love you anymore, you shouldn't have to wake up day after day after something like that. how exactly does one breathe again?