On Aug. 22, Jennifer Garner took her estranged husband Ben Affleck to a treatment center

For Jennifer Garner, nothing is more important to her than her three kids — Violet, 12, Seraphina, 9, and Samuel, 6 — and she will do whatever it takes to make sure Ben Affleck gets healthy so he can be there for them.

Although the couple announced their separation in June 2015 and filed for divorce in April 2017, on Aug. 22, it was Garner, 46, who drove Affleck to a Malibu treatment center when it became clear he was drinking again and needed help.

EE British Academy Film Awards, Winners, Royal Opera House, London, Britain - 10th February 2013
Jennifer Garner and Ben Affleck
| Credit: David Fisher/Rex USA

When it comes to talking to her children about their father’s addiction issues an insider says, “there are no secrets, and Jen is great at explaining what’s going on in ­age-appropriate ways. She tells them Ben is sick and needs doctors. What she ultimately cares about is his sobriety and whether she can rely on him to co-parent. She is trying to keep the father of her children alive.”

A source says the current situation with her estranged husband has been “very stressful for her.”

For more on Affleck and Garner check out this week’s issue of PEOPLE on newsstands Friday.

On the day he went to treatment, Garner arrived at Affleck’s L.A. home twice leaving upset and shaking after the first visit. When Garner returned, she, Affleck, 46, and addiction therapist drove off to the treatment center. “It’s devastating for her to have to stage an intervention in the middle of the afternoon, pretty much in public. But this was a crisis situation,” says a source.

Jennifer Garner and Ben Affleck
| Credit: Pascal Le Segretain/Getty; Axelle/Bauer-Griffin/FilmMagic

Affleck went willingly and has said in the past he wants to be there for his kids. In March 2017, he revealed on Facebook that he had once again completed treatment, writing, “I want to live life to the fullest and be the best father I can be. I want my kids to know there is no shame in getting help when you need it.”

If you or someone you know is in need of help, please contact the SAMHSA substance abuse helpline at 1-800-662-HELP.