Originally Posted by
NickB
Marriage or registered partnership, at least in those member States that recognise the concept. Also to some extent, other forms of established long-term partnership can create some immigration rights, but we are entering the grey zone there.
In the Netherlands, just declaring in front of an immigration official that Mr/Ms XYZ is your "partner" can be sufficient. That is exactly what I did to sponsor my partner to become legal here. There is no need to be married or to enter into a registered partnership. So the OP's girlfriend could sponsor the OP (assuming she is legally residing in the Netherlands, her income is sufficient and her/their house is big enough)