I romanced Liara in ME1 and kept with her in ME2 (her DLC was amazing). I'm now in ME3 and have done the main Citadel quest. She asked if we are still together and I said absolutely. But then each time I talk to her she barely says a word. In ME1, there was only new dialog with her after each main mission. Not sure if ME3 is like that or not. Does it get better? Right now it feels like we're barely together.
I think there's a couple of possible reasons:
That's the limitation of the romance dialogue within the game. Only so many lines of spoken dialogue were dedicated to this.
The pacing of the relationship and dialogue options are going to leave options for those players who made other choices in the previous games. They are also tied to major plot events as triggers, so as you have noticed that when you complete a main plot mission, there is unique dialog, and with the romantic interest additional unique dialog. The rest of the time, not a whole lot of interaction. Anyone romancing Garrus in ME2 can tell you about how many interactions with that character ended with weapons systems getting calibrated. At the rate he was calibrating you could have shot the Kett in Andromeda with some accuracy.
In ME3, there are unique dialogue interactions in several places tied to missions, and some of it differs if you are in a romance with a character that you interact with. But most of the dialogue and events in the game are heard even if you didn't have a romance with the character.
