ex-wife's has a business, can duplicate the same product

There is no patent, which means you can duplicate the product without violating any patent law. You still need to be careful of passing your product off as your ex-wife's product, intentional interference with business opportunities, intentional interference with contractual relations, and a number of other unfair competition laws that may stem from your familiarity with your ex-wife's business. Without knowing you, I would worry that you looking to create emotional turmoil in an already fractured relationship, which has a risk of clouding your business judgment moving forward.  Legally and emotionally, it would be healthier to get in a business unrelated to your ex-wife.