If messaging strangers on Facebook to expose someone is a cyber crime

A guy persuaded a girl (my friend) to an affair and used her in every way by false promises of marriage. That girl even gave money and helped him get into a college in abroad. During his course completion he suddenly by giving a futile excuse stopped talking to the girl and blocked her. She got distressed n upset. She went abroad alone to meet him one last time, but still he didn't meet. The girl is depressed, humiliated and suicidal. After his course he got job there. And the guy's father recently posted on Facebook about how proud he was of his son's achievements. I want to message all those people who liked and commented on this post about what that guy did to that girl. How he used her and ruined her life. My question is : If I message those people in Facebook to let them know, is it a cyber crime? Could I get convicted?