Hilary Duff and Mike Comrie [Photo/Agencies]

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The couple - who announced their split last week - reportedly sought professional help over the course of 18 months in a bid to save their three-year union, but decided to part ways after failing to reignite the romance in their relationship.

A source revealed to Us Weekly magazine: "[Hilary] felt that [Mike] didn't put enough effort into the relationship. Recently he wasn't doing any of the things they'd worked on."

Insiders claim the couple's marriage took a turn for the worse when Mike, 33, was forced to retire as a professional hockey player after suffering a career ending injury in 2012. His situation allegedly put a strain on their relationship.

Hilary, 26, and Mike split amicably and are trying their best to remain cordial, with sources claiming "they are better as friends."

Most recently the couple were spotted out at brunch with their 22-month-old son Luca in Beverly Hills just two days after news of their split went public and Hilary revealed they were together on the day of the announcement.

In a statement posted to Twitter last Friday, she wrote: "Mike and I are sitting here. We are so appreciative for all of your kindness & well wishes. Not an easy day but we're getting thru it together. (sic)"