Malcom Graham, 75, of Skegness Road, Stevenage, took advantage of his friendship with a woman, sexually assaulting her in her own home while she slept in 2018.
The victim disclosed the offence to Bedfordshire Police in 2019, and an investigation was launched.
Detective Sergeant Amy Hawkes from Bedfordshire Police said: “This was a predatory attack by a man who posed as a friend to prey on a woman in her own home.