A large majority of the House voted to legalize same-sex marriage, including 47 Republicans. The law is not yet in force; it is now up to the Senate. There the relations between Republicans and Democrats are equal. Vice President Kamala Harris would then give the casting vote, if it comes to a vote. It takes 60 out of 100 senators to vote on the bill.
It is not clear what Republican senators think of the law. More and more Republican states are enacting anti-LGBT+ laws. In Texas, there are even voices to challenge same-sex marriage in the Supreme Court.
That Court is now largely conservative, as a result of which the right to abortion was previously reversed. Since same-sex marriage is regulated in a similar way, it is feared by LGBT+ people that same-sex marriage will suffer the same fate. A national law legalizing same-sex marriage overrides the Court.