Downfall of Domestic Partnership - NJ

Location: New Jersey We are a heterosexual couple both over 62 years of age, living together with some intermingled expenses. Both of us were previously married with our own children and our own assets. I am retiring and can be added to my SO's insurance if we obtain a Domestic Partnership affidavit from the State of NJ. We have remained as two singles to avoid prenuptial agreements, trusts, etc; it seems to be simpler at our age (we met 10 years ago) to just be two single people sharing a home and a life.

The cost savings for me to be on my SO's plan is over $10k per year. I'm just trying to determine the downside. NJ does not have a common law statute so we could continue the way we are without concern for the estate issues. My understanding is DP doesn't bring estates into the mix, so theoretically it would just memorialize the way we are living. Does anyone know the downside I'm missing?

I have a will and some trusts set up for my kids which predates this relationship, my SO has a will. We're not in each others wills.

Why am I concerned? I knew a couple that insisted on getting married in their 60's. One spouse became very sick, was put on round the clock care in an assisted living facility. Ultimately passed but in the process wiped out all of their assets and because of the marriage wiped out the other's assets too. I know that was a marriage but I want to make sure I'm not saving $10k/year for a potentially bad outcome for one of us.

Thanks for any thoughts.