We need our dads to show up for us, as well as our moms. And when the dad is removed from a family, with the SPO, the balance is shifted dramatically in favor of the "mom as the emotional center" of everyone's lives.
Father's day was a day of celebration while I was married. As a single dad, it takes on a slightly different tone for me. I'm not sad on Father's Day, but I am reflective of what has become of my parenting relationship. With two teenage kids that live with their mom, my involvement is less than I would like.