"He's had to endure a lot; he's seen a lot," Selma Blair tells PEOPLE about her son Arthur, 8

When Selma Blair was diagnosed with multiple sclerosis (MS) nearly one year ago, she had to recalibrate her life in almost every way.

Since her diagnosis, she experiences daily ups and downs living with the chronic neurological disease, never knowing what to expect from her mind and body when she wakes up every morning — aside from doting on and maintaining a schedule built around her 8-year-old son, Arthur.

Blair, 47, says she is honest with Arthur (his father is fashion designer Jason Bleick, whom Blair dated from 2010-2012) about her new challenges and is constantly impressed by his resilience.

“He’s had to endure a lot; he’s seen a lot,” Blair exclusively tells PEOPLE in the latest issue, including watching her fall down stairs or rush to a bathroom if she’s feeling sick.

  • For much more on Selma Blair and how she’s living with MS one year after her diagnosis, pick up the latest issue of PEOPLE, on newsstands Friday

But Arthur doesn’t view his mom’s weaknesses negatively, she says. “He says, ‘Mommy’s not sick. Mommy’s brave.’ ”

The actress says she was recently surprised to learn that Arthur enjoys having her visit his school.

Selma and Arthur
Selma Blair with Arthur and their dog Pippa
| Credit: Carter Smith

“He said, ‘I love when you come to school because you make the kids laugh and you answer all their questions,’ ” she recalls. Blair says she doesn’t shy away from explaining to the kids about why she “walks and talks funny.”

Watch the full episode of People Cover Story: Selma Blair streaming now on PeopleTV.com, or download the PeopleTV app on your favorite device.

“I explain what’s happening and that my voice doesn’t hurt, and we have really decent exchanges,” she says. “I had no idea Arthur was proud of that. I thought ‘I’m probably an embarrassment,’ but to know I’m not was one of my proudest moments.”

Blair says Arthur has a great sense of humor and the two of them currently enjoy one-sided games of dodge ball.

Selma Blair and son Arthur
| Credit: Alberto E. Rodriguez/WireImage

“We play dodge ball, but I don’t dodge because that could be so dangerous,” she says with a laugh of her unsteady reflexes. “Maybe in the future for sure, but I don’t move side to side perfectly, and so I get to just hit him and then he throws it back to me, really chivalrously. And then I get to hit him again, and he thinks it’s amazing.”

“I’s fun and it feels good to him,” she says. “To me too.”

Blair says Arthur’s dad has also been a huge help and that the two of them are happy co-parents.

selma Blair
Credit: Carter Smith

“We have a flexible custody arrangement and Jason is a huge part of Arthur’s life,” she says. “He’s shown up in a big way. I’m really proud of us.”

The actress adds that living well for her son is the driving force in her life, and keeps her motivated in the best way.

“This is it. The only life we get,” she says. “My disease isn’t a tragedy, but I tell myself, ‘You’re going to live in a way that would be an example for yourself and your son.’ ”

Blair’s new series Another Life launches July 25 on Netflix.