bedfellow
/ˈbedˌfeləʊ/noun
1- a person who shares a bed with another同床的人。
1.1
- figurative a person or thing allied or closely connected with another〈喻〉盟友, 搭档; 配套的东西：
big business and politics were inseparable bedfellows.
大企业和政治是一对不可分割的盟友。