Paul Milne, 23, died at Glasgow's Gartnavel Hospital, leaving his family and friends devastated.
His mum Phyllis, 54, of Hamiltonhill in the north of the city, today told of her "beautiful boy".
Speaking exclusively to the Evening Times, Phyllis said: "Losing Paul was a terrible shock. It still is.
"It feels like we are living someone else's nightmare. He was my life. I don't know what I'll do without him."
Electrician Paul, who needed 20 pills and twice-daily physiotherapy to get through each day, was admitted to hospital in October.
Phyllis said: "We knew Paul was really ill – but he managed to battle on for another five-and-a-half weeks.
"He had contracted pneumonia, and another infection, and it was just too much for him.
"He was in a lot of pain at the end, but never complained. Paul was so brave."
Paul passed away on Wednesday last week.
But his family, including dad, Alexander, 53, sister Jenna, and 15-year-old step-sister Simone, have happy memories of the former Cleveden Secondary pupil, who studied electrical engineering at Clydebank College.
Jenna, 27, said her brother was a "fun- loving guy" who "lived for the moment". The administration assistant added: "Paul never let cystic fibrosis stop him from doing what he wanted, I couldn't be more proud of him."
Paul, who was a Celtic fan, travelled around the world, watching his team.
Phyllis said: "Paul loved going off on holidays, including Ibiza earlier this year, with his friends.
"He would travel abroad to see Celtic play too and went to T in the Park most years. He was determined to enjoy every minute."
Since he passed away, Paul's family has been inundated with cards.
Phyllis, said: "It is comforting to know how loved Paul was. I never thought I'd have a son who touched so many lives. I'm so proud of him."
Yesterday, Paul's family held a celebration of his life in Maryhill and hundreds of his relatives and friends packed into the Glasgow Crematorium to say a final farewell
Donations raised will help fund research into treating and finding a cure for cystic fibrosis.
Phyllis said: "Instead of sending flowers, I've asked Paul's family and friends to donate to the Cystic Fibrosis Trust, in his name.
"We want that to be part of Paul's legacy. I just hope a cure for CF can be found, so that no other families have to suffer like ours is now."
To donate to the Cystic Fibrosis Trust, in memory of Paul, visit www.cftrust.org.uk/help/howtodonate or call 0300 373 1040.