Over the last 13 years, I’ve walked my son through cancer twice. More than a quarter of his 24 years have been spent on one goal—knocking leukemia on its butt. And that’s not counting the years of cleaning up the fallout of all that chemo and radiation. Kyle’s first treatment plan lasted over three and a half years. After I recovered from the shock, I zipped from anxious, to uncertain, to alarmed, to discouraged about 20 times a day. Watching him struggle brought on a sadness so deep my chest constantly ached. But every time I thought I’d tumble over the edge, a sense of calm caught me and held…