How death was a severe setback for the Confederacy,on May 10 1863 ?

Wasn't general Stonewall shot by his own men by mistake?

That is correct, SSG Leo Bell. He and his aides were returning from a scouting mission after the Battle of Chancellorsville when some of his troops mistook him in the dark. He was shot three times, resulting in his left arm being amputated the next day. Pneumonia set in and he died a week later, on 10 May 1863.