Article 12 says: "Men and women have the right to marry and to found a family according to the national laws governing the exercise of this right".
This only applies to marriage, not to cohabitation or civil partnerships. It also only applies to heterosexual marriage: the Convention does not require a State to grant same-sex couples the right to marry. But transsexuals may marry in their new gender. Marriage laws may vary from State to State, for example, on issues like marriage with relatives as well as same-sex marriage.
Issues under this article are unlikely to arise for police, but more likely for registrars, and for prison officers. Although recognising the right of prisoners to marry, the Court has nevertheless not found a right to conjugal visits for prisoners in Article 12 to enable them to found a family (but more than half the member States allow this). Cases of separation of spouses under deportation or immigration rules will usually be dealt with under Article 8, not Article 12.