If a married person neglects to plan for his or her estate, the law oftentimes will operate in a way that protects the spouse. When the married person passes away, by law a large portion of the estate, if not all of it, will automatically be given to the surviving spouse. It is assumed that the deceased would have wanted his or her spouse to have the proceeds of the estate. However, the same legal assumption is not made for unmarried couples, even if they have lived together for decades. This makes it even more important for unmarried couples to plan for their estates than it is for married couples.
Investopedia published an article, titled "Estate Planning Must-Haves For Unmarried Couples," that details some of the documents unmarried couples should have to protect their partners. It includes property titling, life insurance, retirement plans, wills and healthcare advance directives. While the full list may not be necessary for all couples, that determination actually hinges on what a given couple actually needs, and that depends on what the couple has and what their estate planning goals are. In some cases, couples may not want life insurance, for example, or they may wish to focus on getting a trust instead of leaving property division in a will.
The important point is this: if a member of an unmarried couple wants his or her partner to have a portion of the estate, then estate planning must be done. The law will not protect the surviving partner in the same way that it would protect a surviving spouse. However, individuals can do so with good estate plans and the counsel of an experienced elder law or estate planning attorney.
Reference: Investopedia (undated) "Estate Planning Must-Haves For Unmarried Couples"