At least you know now that he can be in public places, so now you know if you host an event don't make it at a public place. I know that stinks, but it will be ok. I agree, listen to your gut. However, how will it affect your children to let him host it? I think it is important to know you will be seeing him in public places and will have to wrap your mind around it. I know it stinks and it's not fair. However, there is nothing you can do at this point to change that, so what can you do going forward. How can you handle seeing him. There will be lots of people there. Keep yourself in sane mind. You say he is not going to hurt you while there. Can you bear it to just ignore him?
I don't have the answers, just trying to help you sort out how to deal with this in the future and hate to see all of your work ruined.
God Bless my friend.