They'd been together for 18 years and their relationship had weathered the vagaries of making it in Hollywood.
In the end, according to new reports published Wednesday, two things drove Jon Hamm and Jennifer Westfeldt apart: The Mad Men star got sober and he wanted kids.
Throughout their time together, friends told, Westfeldt, 45, had looked out for the actor, 44, who enjoyed a party lifestyle and had 'taken care of him.'
Scroll down for video
Differences: Sources close to Jon Hamm and Jennifer Westfeldt claim they split because he wanted kids and she was tired of being more of a mother to him than a girlfriend. They're pictured in New York in July, their last public photo as a couple
A source who worked closely with Hamm told the publication that the actress and screenwriter grew tired of feeling more like a mother than a girlfriend.
'He has always had demons and needed a mother figure in his life,' the source told People.
'It was generally assumed that they would break up once he got sober, because he didn't need to lean on her to take care of him so much.'
Turning point: Reports published Wednesday suggested that Hamm's decision to seek treatment for alcohol abuse earlier this year led to a different dynamic in the 18-year-long relationship. He's seen here in Hollywood last week
Formal announcement: Rumors about the state of the couple's relationship had been swirling for weeks and on Monday they issued a statement confirming their split. They're pictured in December 2014
Although it seems the couple tried to iron out the cracks and find a way forward together, ultimately they decided that going their separate ways was the right decision.
'He felt guilty because Jennifer stood by him for so long when he dealt with his alcoholism. It's sad,' an insider told.
As sa single sugar mamas time went on, the difference in their attitudes towards starting a family also began to take on bigger proportions.
'There's always been a rift,' a source close to Westfeldt told. 'Because he wanted kids and she didn't.'
Hollywood couple: Hamm and Westfeldt were jobbing actors in LA and had been together for a decade before the actor was catapulted to fame as Don Draper in AMC's Mad Men that debuted in 2007
The magazine quoted an interview Westfeldt gave to the in 2012 where she acknowledged she'd always thought that one day she'd have children but that life simply hadn't worked out that way.
'My life has also gone in a million ways I never anticipated,' she said in the interview. 'I kept feeling like I'd wake up with absolute clarity, and I haven't.'
She added that she and Hamm had 'a pretty great life together... No one's had to give up an opportunity they really wanted.'
Career focused: Westfedlt pursued her interests in screenwriting and directing during their time together. In 2001, she co-wrote and starred in Kissing Jessica Stein and in 2011, she wrote and directed Friends With Kids that she also starred in with Hamm
For his part, the actor who found fame as Madison Avenue ad man Don Draper, told in 2010 that the Friends With Kids director was 'the love of my life.'
They were both in agreement over their decision to not marry, he said.
Hamm and Westfeldt, who were last photographed together in New York in July, started dating in 1997.
The pair were hit by rumors of trouble back in April, when InTouch magazine claimed the actress had ended the relationship before Hamm sought treatment for his alcoholism.
It was a claim they denied.
On Monday, they formally announced the end of their relationship with a brief statement.
''With great sadness, we have decided to separate, after 18 years of love and shared history,' they said.
'We will continue to be supportive of each other in every way possible moving forward.'
Suportive exes: Hamm and Westfeldt, pictured in March, started dating in 1997. They said Monday that their decision to separate was made 'with great sadness'