The pair, who were together since 2009 and have a two-year-old son called Leighton, together, announced the end of their relationship last week.
Stacey, 24, who also has a six-year old son called Zachery with her former partner, is 'devastated' by the break-up.
The singer and TV presenter told friends she was forced to end the three-year engagement due to 26-year-old Aaron's lack of commitment and failure to settle down.
A source said: "Aaron found it hard to adapt to Stacey's role as a mum-of-two and the sheer scale of work it involved.
"He struggled with their new routine after having a baby, especially as he's in his mid-20s and seeing all his mates going out and having fun."
In October 2012, Stacey said: "In my lovely, fun, fantastic brain, I would really like to get married next year, but Aaron's the more laid-back sort of bloke saying, 'Oh, it doesn't really matter does it? We'll wait a few years.'"
The source added: "Stacey basically wanted the fairytale. She wanted Aaron to be her husband and to be there for the kids, to complete her domestic family set-up.
"'But he wanted fun and the Stacey he first met on holiday four years ago. He couldn't commit to what she wanted, so she knew she had to move on."
To read about Stacey's thoughts on being a single mum again, pick up a copy of Reveal magazine, out now.
Celebrity splits of 2014:
Copyright: WENN Apega