Why do I cry?

My step-brother and mom are screaming at each other downstairs. They do it all the time. I don’t know why but yelling always triggers me. Makes me cry and sob even though it might have nothing to do with me. Does that happen to anyone else? And why does it happen? It makes me feel weak but it’s entirely involuntary. I have an ache in my chest that yearns for a healthy family. I miss my dad.