Sean Garinger, former star of MTV’s 16 and Pregnant, has tragically died after a freak accident involving an ATV. He was only 20, RadarOnline.com can confirm. The reality alum, a father of two children shared with ex Selena Gutierrez who also starred on the Teen Mom spinoff, was moving the all-terrain vehicle from one parking spot to another in front of his home in Boone, North Carolina, when the shocking tragedy unfolded on Feb. 28. “I was with him when it happened,” his devastated mother, Mary Hobbs, shared while recounting the incident. Hobbs said that she was going to back her own car into…