I'm a hypocritical piece of poo-poo for not actually executing this in anything, but...
Miscommunication is a beautiful thing.
You use how character's perceive how something is said/done as motivation behind a action.
(I.E
A: I love Nyanners!
B: (Oh! I know what to get them for their birthday!)
Cue Person B standing with a dumb, wide, self-satisfied grin in front of Person A, with a basket filled with bananas and banana-related merchandise, all the while A is completely confused unaware that someone put ALOT of thought into them.)
To reach a specific point in a plot, influencing how one character thinks of the other would be pretty good. Maybe difficult, but worth it if you plant the seeds of thought early in your characters.
In my honest, one-sided love is pretty trite, but you mentioned rounded characters, and that can be a good work around.