is it ok to attend ur ex girlfriend's wedding?
Its better not to attend. It would be more comfortable for both of you. Your presence would make you in the "hot seat" coz u cannot avoid some people would talk about your "past" with the bride. Let that special moment for the couple only and for you to avoid that feeling of "regrets" if you still felt something for your ex GF.
It depends on how u broke up, but it would be better to avoid it so as to make her feel more comfortable, except if she is the one that actually invited you and made u promise u will be there, even at that, u shudnt be too close to where she is or something, its her day, do not make her feel uncomfortable