If an engaged couple has lived together for years and shared expenses, how are they categorized?

The engagement of the couple, along with their years of sharing expenses and living together, falls under the definition of cohabitants. Cohabitation typically refers to an arrangement where an unmarried couple lives together and shares a domestic life, often similar to that of a married couple. This term encompasses both emotional and financial aspects of the relationship, highlighting the partnership formed through their life together.

While the couple may be referred to as fiancés due to their engagement, the term 'fiancé' specifically indicates their intention to marry and does not necessarily describe their living situation or the shared responsibilities they have developed. The term "domestic partners" is often used in certain legal contexts to signify a similar committed relationship, but it may not apply universally or may require registration, which is not mentioned in the context of this question.

Therefore, identifying them as cohabitants best reflects the practical and social aspects of their living arrangement.