It probably depends on some of the other details involved, such as your age and the circumstances of your parents splitting up.
For example, if you are still a minor, then your duty to honour your parents is greater than when you are an adult, and even if you think your father is in the wrong, you should perhaps respect his wishes nonetheless… I’m not saying you should definitely go, but you need to give it fair consideration and perhaps the advice of trusted priest or older friend.
If your attending this event will greatly upset your mother, and perhaps she was the one wronged when they split, then I can understand your not wanting to go. This would make it very hard.
Then again, as per the previous post, you don’t want to burn your bridges. You don’t need to approve of your father’s actions in order to live harmoniously as a family. You have made your point by not attending the wedding. But there’s no reason to continue to ostracise his new wife, as hard as it may be to accept her.
Offer this one to God, that He may grant you the wisdom to best deal with this imperfect situation…and I’ll offer a prayer for you too.