From Law wiki, the wiki for law research

C-59/85. Ms. Reed was the unmarried partner of a UK national working in the Netherlands, who was refuse a right of residence by the state on the basis that she was not a family member of a worker who was exercising a right to Free Movement Of Workers. Regulation 1612/68 limits family rights of residence to the spouse and dependents, and it was conceded that 'spouse' meant a married partner.

However, the ECJ -- on a recommendatation from the Commission -- ruled that the right of a worker under Regulation 1612 to enjoy the same 'social advantages' as a national was not limited in its generality by the right to be accompanied by his family. That is, there could be rights of accompaniment in addition to those granted in respect of family members. Clearly the ability to be accompanied by a partner, married or otherwise, would be a 'social advantage', and something that would encourage Free Movement Of Workers.