More than three years on, the pair are settling into married life in Broadfield following their wedding earlier this year.
Marilyn, who was married when she met William, said: "I knew it was wrong. Not only was he my son's friend but he was only 16."
Five years earlier, Marilyn was diagnosed with chronic fatigue syndrome and scoliosis, which causes a twisted spine.
She said: "After falling ill, my relationship crumbled. After 18 years of marriage we slept in separate rooms and I became lonely and withdrawn.
"William saw how I used to struggle with day to day things like shopping and offered to help.
"His sense of humour helped me a lot. Over time we became attracted to each other."
Marilyn, who has eight grandchildren, tried to fight her attraction to William, who is now 20.
She added: "William and I stayed strong but one day, when I was feeling particularly ill, I was so weak that William had to help me get out of bed.
"As he lifted me up there was a moment between us and we kissed.
"It was magical but afterwards I felt terrible."
Marilyn said they should not see each other again but William refused and the pair began a secret relationship.
When Marilyn's divorce went through, her husband moved out, William moved in and her children had to find out the truth.
One of her daughters moved out and her son Mark, who had been William's friend at Thomas Bennett School, called her a "paedo".
Marilyn said: "It got very hard because I felt I was losing my family. It tore me apart.
"I know 30 years is a big age gap but William and I have so much in common."
"We truly are soul-mates. I know it is difficult for other people to understand, but slowly both our families are learning to accept us as we are."
William added: "You take the good with the bad. It has been quite difficult but we kept going."
William asked Marilyn to marry him several times before she finally accepted on her birthday in February this year.
They were married in April and their honeymoon took them to Gibraltar, where Marilyn grew up.
