The "handsome lass" is a very handsome Sim named Lassiter something or other. My queen was quite smitten with him and wanted to marry him anyway, but I thought it would be better to marry a prince. Silly me. Anyway, I let her marry him and they are SOOOO cute together! Always hugging and doing kissy face ever when I'm not playing them.
In this next go 'round, my queen married the heir to Effonmont, not quite so romantic and the morose dude is just a pain. You can convince them to have somewhat of a romantic interaction but so far no whoo hoo allowed by the game. In her Genie quest I still had her ask for a handsome lass, hoping this time she would also be able to marry Lassiter. (He really is a great guy). Unfortunately, as too often happens in RL, her duty to the throne had her marrying the elf prince of Effonmont. (Which, by the way, does not keep the loyalty level high!)
My Frgo (frog prince), is interested in my merchant, (not my doing), but she is totally involved with my very handsome knight who I intend to be my next country's king. They are only romantic interest but romantic interest will prevent a marriage from happening, or even allow the choice of ask to marry.