What do you think or do if your Sim suddenly flirts with someone that you don't like?

I don't take idle flirting too seriously since it happens so often and indiscriminately but I like to leave it up to chance who my sims end up with. Any time I've tried to plan out romances the sims quickly end up having better chemistry with exactly the opposite of the person I wanted. I'm not too controlling of who they choose as long as it's entertaining, hideous goblins included. But it does bother me when I find my already married sims with random crushes.