I suggest that the single most important thing for you to remember is that Z refused to do anything to harm you. Should she have alerted you-and the police? What seems obvious to all of your readers is anything but obvious to someone who is young, abusing drugs and possibly fearful of retaliation. It is easy to demand that other people be responsible and brave. I suggest you reflect on how all of the people in your social circle viewed the world and their place in it at that time. I suggest that you may then be able to forgive Z. Publicly available research tools can let you find out about what the creep has been doing in the intervening years-and if there are steps you can take that may harm him more now than you could have done back then.