I wouldn't doubt that he's a multiple abuser.
Don & Huck both mention grooming, it's what they do. They pick us out, they smell vulnerability and loneliness and lock onto it.
Huck mentions perp's choosing professions just to be near children, he's right.
I went to a boys boarding school where I was abused by one teacher, but I know there were many others, some "left" mysteriously overnight never to be seen again. Others were there for many years, and deeply suspect.
What your BF does about this is his choice, but he's started the ball rolling, and I hope the authorities pick it up and run with it.
If the teacher is still drawing breath then he's fit enough to end his days inside jail.
It makes me very sad and angry to think how many others are suffering for what these bastards did.
Go confidently in the direction of your dreams! Live the life you've imagined. As you simplify your life, the laws of the universe will be simpler.
Henry David Thoreau