We can't take our eyes off this couple! Frankie Valli, the falsetto-voiced frontman of the Four Seasons, best known for his hits "Sherry," "December, 1963 (Oh, What a Night)" and "Grease", married longtime love Jackie Jacobs in Las Vegas Monday at the Westgate Hotel, ET confirmed. Speaking to the People following the loved-up affair Valli said, "It's…