same-sex partner
Refers to a romantic or life partner of the same sex. Used in contexts such as LGBTQ+ relationships, legal partnerships, and social recognition.
He lives with his same-sex partner.
The company provides family allowances to same-sex partners as well.
same-sex partnership
Compound of 同性 (どうせい, 'same sex') and パートナー ('partner'), a straightforward modern term.