Some friendships form through shared experiences at school, others through a soccer club or workplace. For Jan Wolfenstädter and Tina Kunath, their bond began with her diagnosis. Kunath was 8 years old when doctors found she had blood cancer. She needed a stem cell donor and found one in Wolfenstädter. He also became a lifelong friend. Their friendship is extraordinary, say Tina Kunath, now 21, and Jan Wolfenstädter, now 34 years old. “You realize that you are connected in a different way,” Kunath told dpa as she sipped a mint tea in Cologne. Wolfenstädter sat opposite, nodding as he nursed a …