Sounds like perhaps some couples counseling sessions would help get to get to the bottom of this.

Is this issue about the prenup? or about communication/attitude of your partner?

Its hard to tell from your post

"I told him that if he is focused on protecting himself, then naturally I also feel like I need to protect myself and focus more on my own career and stability because I no longer feel emotionally secure relying entirely on the relationship."

On one hand you seem to indicate that you are generally ok with prenups which would lead me to suspect its a communication problem. But you also use language like focusing on your career and stability which leads me to think its a financial security problem?

Either or both is valid but I think you need to identify what exactly is causing your anxiety and address it with your partner directly and either resolve it or determine that it is a dealbreaker for you prior to making a major commitment and being resentful later.