Kevin Costner's Work Schedule Was 'Hard' on Wife, Says Source: 'She Wasn't Happy About It' (Exclusive)

Kevin Costner's demanding work schedule was difficult for wife Christine prior to her divorce filing.

Amid the pair's breakup after 18 years of marriage, a family source tells PEOPLE that while the Yellowstone actor, 68, "knew" Christine, 49, was "unhappy," her divorce filing came as an "unpleasant surprise."

"Christine wants them to spend family time at their Santa Barbara home," the source says. "During filming, Kevin is not around very much. His absence has been very hard for her."

According to the source, "Christine doesn't want him to throw himself into another project. He has been obsessed with filming Horizon since last year. She wasn't happy about it."

A separate entertainment source tells PEOPLE that "at times, his career has taken precedence over his home life."

"Kevin hasn't been home very much for quite some time due to filming, the popularity of Yellowstone, and the time necessary for his other projects. He has been in demand," says the entertainment source.

"All of this success and excitement over the new project probably took his attention away from his family more than he realized. Since it didn't look like that would change and likely could get worse, it caused tension at home," the entertainment source adds.

Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.

Christine had filed for divorce from Kevin last week, listing their date of separation as April 11.

"It is with great sadness that circumstances beyond his control have transpired which have resulted in Mr. Costner having to participate in a dissolution of marriage action," a rep for the actor told PEOPLE last Tuesday. "We ask that his, Christine's, and their children's privacy be respected as they navigate this difficult time."

The pair married in September 2004 and have three children together: sons Cayden, 16, and Hayes, 14, plus daughter Grace, 12. Kevin also has four older children — daughters Annie and Lily and sons Joe and Liam — from previous relationships.

According to a source, Kevin, who split from first wife Cindy Silva in 1994, didn't want the divorce.

"It was not anything that he wanted or sought," the insider said. "And if he could change the situation, he would."

RELATED VIDEO: Kevin Costner's Wife Christine Files for Divorce After 18 Years of Marriage

Paramount announced on Friday morning that Taylor Sheridan's hit Western series Yellowstone, starring Kevin, will end after the upcoming fifth season, which is set air in November (pending a swift resolution of the Writers Guild of America strike).

But the actor and handbag designer's split "has nothing to do with Yellowstone," a source told PEOPLE Friday.

"The two situations are unrelated," the insider emphasized.