Who is Dan from Next to Normal and what is their importance?

Dan is Diana's husband, around the same age. He loves her deeply, still desires her, and unconditionally supports her in her struggles. He is also worn and weary by having to cope with her unpredictable mood changes, her surges of active energy and her crashes into despair. While he appears, on the surface, to be self-effacing and humble, there is the sense that he is also somewhat self important, in that he repeatedly refers to himself as the only one who truly cares about Diana, the only one who has stuck with her through all the difficulties of her life. In many ways, and although he appears to accept her condition on her terms, he insists that she be his wife on his terms - seeing the doctors he wants when he wants her to, taking the treatments he wants when he wants her to and, in the second act, remembering their shared past in the way he wants her to. He is, in many ways, passive-aggressive, disguising his need to control with apparent compassion. Over the course of the narrative, he moves from this way of interacting with his wife into not only a more genuine compassion for her, but also a greater understanding of himself. He realizes how much he has denied the suffering of his past and, like Diana, prepares to move into the future with a greater sense of both honesty and possibility.