He is being a dick, so turn yourself into a bigger dick?
Fighting back is not being a dick.
Document all interactions? Wtf kinda bullshit is this.
Documenting all interactions gives OP the necessary resources to transform this into a legal matter, if OP so desires.
Having and nurturing a grudge against that guy does not help you in any way.
Not fighting back will likely end with OP feeling like shit, with a bigger grudge towards the bully and himself for not acting.
Ignore him and live your own life happily. Not worth wasting your time and happiness like that.
Did you even read the OP??? This shit has been going for TEN YEARS. OP already tried to ignore him, it did not work; OP already tried to contact him in a friendly way (congratulating him for the grad), and it did not work either. Odds are that this shit will go on until someone forces the moron to stop.
That what you naive pacifists don’t get - “just walk away lol! how hard it is lmao!” does not always work. It won’t make the bullying “magically” stop, nor “magically” prevent the psychological damage to the person.