Many riddles are based off of love and romance. A number of these explicitly end with the word "love," while others require more advanced word play.
Two examples of riddles about love are "What is invisible and makes people sweat and feel anxious, yet people can’t survive without it?" and "What makes grown men cry, but humanity would go extinct without it?" Similar riddles can be created by listing any extreme affects of love on people's behavior. For more comical riddles with puns, there is the question "What did the painter say to his/her boyfriend/girlfriend?" The response is "I love you with all my art."