Ashton Kutcher and Demi Moore
11/18/2011 AT 03:30 PM EST
and Ashton Kutcher announced their split
on Thursday, but tensions have been building for some time.
"Ashton is unhappy; [Demi]'s unhappy," a source tells PEOPLE. "It just got to a point where they had to end it."
Despite longtime problems, the exes did try to work on their relationship. Unfortunately, their issues – which went beyond Kutcher's alleged infidelities
– couldn't be resolved.
"The fighting could get pretty intense," an additional source says of Kutcher, 33, and Moore, 49. "Whatever counseling they did was fine for a quick fix but could not get to the heart of the problem."
For much more on Demi and Ashton's split, pick up the next issue of PEOPLE magazine