Does smoking really shorten your life span? and if it does by how much?

well i have a big brother ,he's an adult now, and he smokes. my mom is always bothering him about it and i can understand why but i always thought that it was the persons choice i mean there's no way i'd ever do something like that but he does it to release stress and he never does it like around the family. so i always thought i'd just never bring it up and leave him alone about it but recently my cousin has come to visit and when he found out that my brother was a smoker he told me "he's gonna die 10 years early" and he said it with such a carefree attitude at first i was pissed off then i started thinking about it and i ended up crying in my closet until my brother came to get me, i told him what had happened and he kept saying that he's gonna be okay, but i just couldn't stop crying and now im really worried because just the thought of him dying has me going through a heart attack and on top of that i've had to deal with the loss of my grandmother, my best friend's mom, my best friend, and a couple of family friends. and although i cried for them and felt sad i have a special list of people who i just can't live without and on that list would be my brother, mom, dad, aunt, and a couple others so i just really need advice more than anything else on how i can handle this because if i don't get some answers i think i'll either cry until all the water is out of my body or isolate myself from the world to prevent getting hurt. please if anyone has ANY advice i really, really need it.