Todd Howard has confirmed that only the four main Constellation NPCs will have full romance questlines attached to them.
Speaking on Kinda Funny Games, Howard explained when asked what companions can be romanced that "the four main Constellation [NPCs] are the ones that support full questlines for them, and romance."
It's likely that this will lead to more fleshed-out and different partners, similar to Mass Effect or Cyberpunk 2077, rather than the old Bethesda system which just allowed you to wear a special necklace that then let you stuff whatever bride you wanted into your home.
Still, it does seem rather strange that in such a massive game, our options for developing relations with companions is limited to a few choices, all of which are centred around Constellation, so if you wanted a space pirate husband, you're going to be missing out.
What do you think of Starfield's romance options?