I wouldn't go. It doesn't matter how "alright" your ex tells you she is with you attending his wedding, there is bound to some animosity in the back of her mind. Why give her cause to have more anxiety on her special day than need be?
It's times like this that make me happy that, even though I am still friends with a lot of my exboyfriends, they do not put me in the awkward situation of inviting me to their weddings. I know for sure that one of their wives would have told her husband that it was fine if he invited me and then
completely freaked out when she saw me there. She still really has a complex about me and I don't know why. Oh well! It's her loss
It's your decision, but I wouldn't attend.