Physical & Emotional Abuse Support Group
Abuse is a general term for the treatment of someone that causes some kind of harm (to the abused person, to the abusers themselves, or to someone else) that is unlawful or wrongful. No one deserves abuse, period. Abuse can be emotional, physical, or sexual.
And on the other hand, you write that you want to tell him you forgive him and that you need closure on this. So why don't you write him a letter before you go with everything you have to say to him and don't send it or give it to him? That is for you to first observe what you have inside for him.
Telling him in person that you forgive him will NOT get him out of your head. Healing from abuse related trauma isn't about forgiving the abuser - at least not at first. That would come MUCH later. The total focus must be on you.
disi has a good idea about writing him a letter but not giving it to him. The letter can include things you will/do and won't/don't miss about him, how much he hurt you, etc. Then burn the letter & create a funeral like ceremony around it. You may have to write more than one letter. And that's ok. Just do NOT ever give him the letter(s).
You can also set your intentions that you will not run into him at the trade show. And just in case you do, have a quick exit plan in place.
You asked what its going to take to get him out of your head. It almost always takes therapy with a qualified counselor who understands the dynamics and affects of abuse (not all do) AND has additional training in trauma release and recovery from abuse.
~healing hugs~