Sian's new love, exercise, had mended her broken heart.
So much so, she even worked out on Christmas Day and New Year's Day and took up weightlifting.
Now, more than a year on, Sian weighs a slinky 76kg and wears a size 12.
She posted photos of her ripped body on the internet, so she can inspire other women that were bigger - but said she had no interest in winning her ex back.
Instead, she is on dating app, Tinder - where she has lots of admirers, but has not yet found a boyfriend. Now focusing on her body and career, her self-esteem has soared since being dumped.
She can lift 100kg weights and visits the gym daily for an hour-an-a-half at a time.
Hospital clinic coordinator Sian has also gained an amazing 13,000 Instagram followers, who ask her for dieting and weight loss tips. And she plans to return to college, to train as a personal trainer and nutritionist - something she had never considered before.
'I was so sad when we broke up,' she said. 'But, actually, it was the best thing that could have happened to me.'
Sian hit 120kg, a size 26, while at a make-up college in Northamptonshire in her early 20s.
A self-confessed "party girl", she was "really lazy". "I would have huge portions," she explained. "I would party all the time and eat junk. I'd drink litres and litres of sugary, full-fat cola and loved takeaway pizzas.
'I'd go to McDonald's and get two portions of food.
"I never touched vegetables. It was never-ending." Aware that her weight was rapidly increasing, in early 2015 - while still dating her ex - she made a New Year's resolution to lose weight.
So, she started exercising, but lost interest after a few weeks. "My boyfriend also liked similar food," she explained. "We had similar lifestyles."
Covering-up in oversized shirts and leggings, usually from New Look, Sian always made sure she was perfectly made-up.
"But then when my boyfriend broke up with me out-of-the-blue, it changed everything," she said. "I was sad and worked out on my emotions at the gym.
"I wasn't trying to win him back, I was trying to take my mind off him."
Sian also became interested in healthy eating, tracking her calorie intake with smartphone app MyFitnessPal.
"It really helped," she said of the app that tracks diet and exercise. "I now eat oats for breakfast, lean chicken and lots of veg and protein. "Most of all, I love feeling strong.
"I was fat and sad. Now I'm healthy and happy."
