Jagger has been married (and divorced) once, and has also had several other relationships.  From 1966 to 1969, Jagger had a relationship with Marianne Faithfull, the English singer-songwriter/actress with whom he wrote "Sister Morphine," a song on the Rolling Stones' 1971 album Sticky Fingers. After his relationship with Faithfull ended, he pursued a relationship with Marsha Hunt from 1969 to 1970. Jagger met the American singer and, though Hunt was married, the pair began a relationship in 1969. The relationship ended in June 1970, when Hunt was pregnant with Jagger's first child, Karis. She is the inspiration for the song "Brown Sugar," also from Sticky Fingers.  In 1970, he met Nicaraguan-born Bianca De Macias. They married on 12 May 1971 in a Catholic ceremony in Saint-Tropez, France, and had one child, Jade. They separated in 1977, and in May 1978 she filed for divorce on the grounds of his adultery. During his marriage to De Macias, Jagger had an affair with then-Playboy model Bebe Buell from 1974 to 1976. In late 1977, Jagger began dating American model Jerry Hall; they moved in together and had a total of four children. They attended an unofficial private marriage ceremony in Bali, Indonesia, on 21 November 1990, and lived at Downe House in Richmond, London. During his marriage to Hall, Jagger had an affair with Italian singer/model Carla Bruni, from 1991 to 1994. She went on to become the First Lady of France when she married then-President of France Nicolas Sarkozy. The marriage to Hall and the marriage ceremony were declared invalid, unlawful, and null and void by the High Court of England and Wales in London in 1999.  From 2000 to 2001, Jagger had a relationship with the English model Sophie Dahl. Jagger had a relationship with fashion designer L'Wren Scott from 2001 until her suicide in 2014. She left her entire estate, estimated at US$9 million, to him. Jagger set up the L'Wren Scott scholarship at London's Central Saint Martins College. Since Scott died in 2014, Jagger has been in a relationship with American ballet dancer Melanie Hamrick.

Answer this question "What was his longest relationship?" by extracting the answer from the text above.
Jagger had a relationship with fashion designer L'Wren Scott from 2001 until her suicide in 2014.