If you get upset while discussing, take a few weeks to communicate and think clearly about what's best for you and your partner. Going to a premarital counselor together could also help with issues that you're having about the prenup and any other prewedding matters too, like children, religion and family issues.
Just like a romantic partnership, a marriage is a financial partnership. A prenuptial agreement is a business transaction within your marriage, so just like any other financial discussion, try to put your emotions aside and think clearly.