"It's not that I don't care. I just don't care to hear about it."
To paraphrase the great "Free to Be...You and Me" song: Bosses are people, people with feelings. Your boss probably does have a lot of empathy for you and the horrible thing going on in your personal life. But your boss has a job, too, and it's not to cry with you in the bathroom. Your job still needs to get done even when you're too distracted to do it. (It's possible that your boss can help you work through your distraction if you are able to articulate what would make it easier for you.)