Technically you're not responsible for either. That having been said, a prenuptial agreement may be something you wish to consider, particularly if you have substantial assets to protect.
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Your asset would generally only be subject to possible seizure if he (1) owed arrears, (2) she got a judgment against him, and (3) you converted your assets to joint names. That said, a prenuptial agreement is the way to go. Schedule a consultation with a NYC Divorce lawyer for a full assessment.
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All other attorneys are correct that a Prenuptial is a great way to go. The point no one else mentioned but comes to my mind is whether it should be drawn by a New York lawyer or a New Jersey lawyer . So I would consider which state gives you a contact that would be more enforce3able in the state that you choose. As both a New Jersey and New York practicing attorney what effect having the laws of their respective state govern the agreement.
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Alternatively, you can simply keep all your assets separate except those that you want in a joint bank account or otherwise jointly. There is no risk to your separate assets unlike a theoretical or actual threat to the joint asset(s).
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