The way Paul Arrouet proposed to Dylan Lauren in Montauk on Sunday, there’s no way she could have said no. After a sporty day of jogging and biking, the squash-playing hedge fund manager invited Dylan, daughter of Ralph and Ricky Lauren, to the beach at sunset, where he’d set up a table under an umbrella with six dozen pink roses. Spelled out in candy for her were the words, “You are my ‘It’ girl.” Arrouet, who has been dating Lauren for four years, got down on one knee, presented her with an emerald-cut sparkler, and said the right words. Dylan — who owns Dylan’s Candy Bar and happens to have a book, “Unwrap Your Sweet Life,” coming out in October — said yes. “We’ve always been best friends. We always have fun together,” she said yesterday. “It’s very exciting.” Her parents joined them on the beach to celebrate. No date is set yet.