I hate it for him. It's a grueling recovery.
Sadly, I've seen it first hand. My oldest daughter tore hers (the first time) just coming to a jump stop her sophomore year of high school. She then tore it two more times in high school, and I think only one involved contact.
Braces help some, but are more psychological when one is returning to play after a knee injury.
Knee ligaments really are the weakest link, and there aren't any exercises, etc that can be done to help prevent them.
It's interesting that females are much more likely to have them than males.