FrostyEditor exposes the files but it is not as intuitive as other games where the flags would be set, had a poke around last night but could not decipher the critical pathways and logic checks that are undertaken to trigger the conversations. I suspect there is a logic check for being in a romantic relationship with someone else which if set to true suppresses the conversation option for other companions. Will have another look later to see if I can find and disable that.
Update:
I may be entirely in wrong direction here but the Systems > Types > persistencegenerated location in the data explorer have the romance states, it seems the *charactername*_00_romance_######### (# being numbers) files contain the FieldCollections that contain the booleans for the quest states, trying to find the logic that sets these / logic that checks these booleans so that if one is set it blocks the path for others.
Update 2: think the above is a wild goose chase. Found this video that am going to help me dig into the files better, https://youtu.be/Y_BOoqRejvc?si=awbCWMw-iy9771h8 specifically extracing xml's, using vscode and resolving the hashed values if I can.