Ceon Broughton, from Enfield in north London, was found guilty of being responsible for the death of the daughter of Taggart and Holby City actor John Michie.
Miss Fletcher-Michie died at the Bestival music festival in September 2017 after 30-year-old Broughton “bumped up” her dose of the hallucinogenic drug 2-CP.
Broughton was also found guilty at Winchester Crown Court on Thursday of supplying Miss Fletcher-Michie with the drug.
He had previously pleaded guilty to two other charges of supplying drugs to Miss Fletcher-Michie at Glastonbury festival in June 2017.
And he was in breach of a suspended prison sentence for two charges of possessing a lock knife and a Stanley knife blade.
Miss Fletcher-Michie’s mother Carol, a former singer with Hot Gossip, read her victim impact statement to Winchester Crown Court, saying: “On the outside we all look much the same as we did before, but inside our hearts and soul have been ripped out, trampled on and stuffed back in.
“Like losing a limb, waking up every day to face this new reality, having to learn to live with this for the rest of our lives.”
She added: “We do not think Ceon is evil. He was stupid, massively selfish and he lied.”
Mr Michie told the court: “I wake up every morning to face life starting again without Louella, our daughter, our sister, our friend, our family now broken.
“For what? It makes no sense, our beautiful Louella should still be with us on any measure of humanity.
“No more yoga with my daughter, no more running round the outside of the Arsenal stadium with my daughter, no more family fun with my daughter, her life cut cruelly short.”
Daisy Fletcher-Michie said she had been diagnosed as having post-traumatic stress disorder and had suffered panic attacks following her sister’s death.
She said: “Our lives have been torn apart by the actions of someone who was supposed to love Louella, the most-loved person I have known.”
Sentencing Broughton, the judge Mr Justice Goose told him: “You were only concerned for yourself. You didn’t want to be arrested, you were more in fear of that than in getting help.”
The prosecution claimed during the trial that Broughton had failed to take “reasonable” steps to seek medical help for Miss Fletcher-Michie.
The jury was shown videos taken by the defendant as her condition worsened – and possibly after she had died.