At present, only same-sex couples can enter into civil partnerships in the UK. Following a successful challenge in the Supreme Court, the UK Government has made The Civil Partnership (Opposite-sex Couples) Regulations 2019. These regulations mean that civil partnerships will be available to both same- and opposite-sex (or 'mixed-sex') couples in England and Wales from 2 December 2019. A House of Commons Library briefing provides the full background to this change. The explanatory memorandum to the regulations explains the situation in Scotland and Northern Ireland.
This change affects the Immigration Rules, because civil partners are able to accompany and stay with Tier 4 students. Wherever in the UK you plan to study or are studying, your opposite-, as well as same-, sex civil partner will be able to join or accompany you, if you are eligible to have dependants with you in the UK - see Dependants. Schedule 1 of the regulations lists the relationships in other countries which the UK Government recognises as a 'civil partnership'.
The tuition fees and Student Support regulations in all countries of the UK will be similarly affected. Civil partners of people with certain nationalities, for example, EU nationals, or with a particular type of immigration status, for example, refugees, can be eligible for home fee status and student finance.