Bo Derek & John Corbett — 18 Years
Better known as Bo Derek, Mary Cathleen Collins is one of the finest film and TV actresses that the film industry has ever seen. She brought the spotlight upon herself with her portrayal of the character by the name of Jenny Hanley in 10 (1979). She also played the role of Mandy Singh Dhaliwal in 5 Weddings (2017).
After her husband had died in 1998, Bo started dating an American actor by the name of John Corbett in 2002. The two of them have been together for about 18 years now, and even though they are still not married, their relationship seems to be working out just fine for them.