When Ross told Emily he loved her, Emily replied, “Thank you.” The moment occurs in “The One with the Free Porn,” after Ross follows Emily to the airport in an attempt to stop her from returning to England.
Ross had been encouraged by Monica to tell Emily how he felt, but his dramatic confession catches Emily off guard. Instead of immediately saying that she loves him too, she responds with a stunned “Thank you,” creating one of the show’s most deliberately awkward romantic exchanges. Ross then returns to New York, believing the moment may have gone badly.
The story does not end with that airport response. Emily later leaves a message saying that she loves Ross, and the two speak by telephone. When Emily tells Ross she loves him, he replies, “Thank you,” reversing the earlier exchange. The couple eventually marries, but their relationship deteriorates after Ross says Rachel’s name instead of Emily’s during the wedding ceremony. The answer is therefore specific to Ross’s first confession at the airport, not Emily’s later declaration.