Should I attend my nieces wedding if my ex is invited?

I have been divorced for over 3 years. The divorce was not very pleasant and my ex has been very confrontational to me and my boyfriend. My niece is getting married in a couple of months and her father (my brother in law) is adamant about inviting my ex to the wedding. The mother of the bride, my sister does not want to invite him. I'm not sure how the bride feels because I have been told not to contact her. The rest of my family would prefer he not be there because he has caused nothing but problems in the family.

I have said that if my ex is invited then I will not attend.