What should I do to punish my abuser ?

at the age of 26, i think it's a bit late for involving your parents. you could, of course, go to the police but, unless he admitted this, i very much doubt that there would be any consequences for him. more importantly, i think you should seek help for your trauma by telling your GP. they ought to be able to get you some sort of counselling in order for you to come to terms with your experience.

for what it's worth, when i was very young i was gratuitously attacked by another boy. some years later i had a nervous breakdown and i've suffered from depression ever since. i have to tell you that i have no desire to punish this boy for what he did. i doubt he really understood the consequences of his actions and i see no point in causing him any problems over something that happened so very long ago. now, i know some people will argue that this is completely different, and perhaps it is. nevertheless, i do think you should focus more on healing yourself rather than punishing him.