Hey girl! First of all, you still have a future with this man...if you want one. From what you have written, he has not done anything wrong. You admit that you two broke up for a brief moment, and unfortunately he "got it in" with another woman, dropped his seed, and now his name lives on. By no means am I dismissing the real issue at hand: your soon to be husband has started a family with another woman before he started it with you.
Do not consider calling off a wedding between you and the love of your life. Perhaps, it is best that things happened this way. Ask yourself, if you found out seven years ago that your fiancee had a baby on the way, would you have easily accepted him back into your life? I know this is a hard pill to swallow, but I believe he loves you and you two still have a great future ahead with having your own children. Now, go and finish planning the best wedding ever. Best of luck with everything!
Ladies (& gents), do you agree? The statement stands true, your past will always catch up to you, so be careful how you play. It is just unfortunate when innocent people get mixed up in your stuff; however, I do not see a reason to cancel the wedding. This is my advice, please don't hesitate to share yours.