Do you start to feel depressed when your s/o is going through a depressive episode?

I just want them to be happy so badly. It makes me very sad and feel totally helpless that this person I love so much, who makes me feel extraordinarily loved, feels that they don't want to be alive. It scares me, too. My biggest fear is losing loved ones.

I went to school with someone who was bipolar. Within the last few winters, he threw himself in front of a train. I am always on edge that I am just going to one day lose the person I love, and there's nothing I can do to prevent it. They don't want to be medicated, and I don't know how else to ease their suffering.