I'm sorry you have been carrying this around for so long. I can't speak for certain, but I know many, many people who have experienced sexual harassment on public transportation, and nobody I know has become self-destructive or addicted to abuse as a result of it

Harassment on public transportation is incredibly common, so I'm sure that if that incident was upsetting to him, he would have a network of people to talk to about it, so he would be able to process it in a healthy manner. I hope you can absolve yourself of guilt about his current state! If you wanted to try to make your remorse constructive, you could always try to find online boards for people who have been groped in public and try to help survivors.