Wiktionary
n. A romantic partner for life. This can be same-sex or opposite-sex, married or without marriage, and monogamous or polyamorous.
Wikipedia
Life Partner is a 2009 Bollywood romantic comedy film. It stars Govinda, Fardeen Khan, Tusshar Kapoor, Genelia D'Souza and Prachi Desai in lead roles. The film is written and directed by Rumi Jaffery and produced by Abbas-Mustan under their banner, Burmawalla Bros. It received positive reviews upon its release on 14 August 2009, though it was an above average grosser at the Indian Box Office
Usage examples of "life partner".
Thinking of her in terms of a life partner would mean completely restructuring how I viewed her and worked with her, and right now she was far too valuable as my assistant for me to rock the boat.
Look at Soloman and how well he has adjusted to losing his life partner.