Finding a synonym for the phrase "spouse equivalent" can be challenging since it encompasses the idea of a long-term partner who shares a deep emotional bond with another person. Depending on the context, some possible synonyms include "life partner," "companion," "significant other," "domestic partner," "common-law spouse," or "cohabitant." Each of these phrases has its own connotations and nuances that may vary depending on cultural, legal, and social contexts. Ultimately, the choice of a synonym for "spouse equivalent" depends on the speaker's intent and the relationship they wish to describe.