The actress, who has been married twice, said she has had her "heart broken quite a lot".
She said: "For me, broken means that feeling of 'I will never ever recover from this'.
"The notion of 'happily ever after' is bonkers. People aren't honest because of the desire to maintain the romantic ideal. I was talking about Alan Rickman's adulterous role in Love Actually and I got into trouble for daring to ask 'Don't you think we might have become desperately punitive about monogamy?'."
Thompson's first marriage was to fellow actor Kenneth Branagh. She then married Greg Wise.