Anyway to remove a romantic interest?

There is a way that I use when I really want to get rid of it. If you have MCCC and UI Cheats installed, you can first right-click on that person in the relationship panel and that will show you their scores, remember them. (e.g. 65,10) First one is for friendship, second is romance, but setting it to 0 will not remove them from the romantic panel. So close that window.
And then delete their relationship with MCCC like this: left-click on them> MC Command Center>Relationships>Delete Relationship> Select your sim or the other way around (this will reset their whole relationship as if they never knew each other). Then introduce yourself again, and use UI Cheats to set their Friendship back to where it was (65,0 for our example).
I hope this little trick is useful to you :)