Reese & Ryan: Was there another woman?

But today, we find out what (or who) may have caused the breakup.

Just two weeks ago, Reese accompanied Ryan to his screening for "Flags of Our Fathers" in New York, where the couple reportedly fought bitterly at the after party.

Sadly, explosive new details are surfacing about Reese and Ryan's troubled marriage, including reports of an alleged affair between Ryan and a young actress.

"Ryan did not go out of his way to hide the fact that he was having a fling with his co-star Abbie Cornish," said Us Weekly's Katrina Szish. "Besides the fact they were spotted making out in a sushi restaurant together, she was spotted many times leaving his loft apartment."

According to Us Weekly, Ryan's alleged affair with Cornish, a 24-year-old Australian actress, was common knowledge around Austin, Texas where the two were shooting the new film "Stop Loss."

Abbie's rep denies the affair and both Reese and Ryan's people had no comment.

"Reese came across pictures of Ryan and Abbie together and she immediately confronted Ryan. He admitted having an affair. He said all of the rumors were true and said let's just end this now," Szish told Access Hollywood.

Abbie, who some say actually resembles Reese, is an actress on the rise. She can be seen opposite Russell Crowe in the romantic comedy "A Good Year," which hits theaters next week, and opposite Heath Ledger in the sexual drama "Candy" which opens November 17th.

Reese and Ryan, who have a 7-year-old daughter and a 3-year-old son, have been plagued by rumors of problems before. Just days after Reese's big Oscar win in March, tabloids were reporting their marriage was in crisis.

"Reese has been holding onto this marriage for dear life, primarily because she loves her children," Szish added.

Ironically, five out of the last eight Best Actress Oscar winners split from their partners shortly after their big win.

This includes Hilary Swank, Halle Berry and Julia Roberts

Both Reese and Ryan have publicly admitted to receiving marriage counseling in the past.

"I don't think there should be a social stigma attached to having therapy," Reese told Access Hollywood in 2002. "It's self improvement."

In 1998, Access asked Reese if it was easier dating a fellow actor.

"I don't know, all I can say is it's great to be with Ryan. He understands me and I think that's all you can ever ask for in a relationship," she told us.