Anne Heche Ex James Tupper Admits to 'Difficult Time' Since Her Death as Friends Gather to Honor Her Life

Anne Heche's loved ones came together to remember the late actress on Tuesday at a reading of her new memoir.

The event was held at the Barnes & Noble at the Grove in Los Angeles, with some of her closest family and friends in attendance, including her Better Together podcast cohost Heather Duffy, Girl in Room 13 director Elisabeth Röhm, actress Justina Machado, ex James Tupper and their son, Atlas.

"I want to say that I'm doing great, but it's been a very, very difficult time. A very big transition and spending time with my boy and looking after him, that's basically been my whole focus," Tupper told PEOPLE at the event.

"It's very difficult whenever you lose a parent like that. Your whole world switches inside out, and I think kids experience trauma in a way that adults don't. Adults have a context to put it in, but kids do not. You want to bury it, you want to forget about it and move past it," he added. "I happened to have lost my mom, too, when I was very, very young. So I kind of understand what he's going through."

Tupper told PEOPLE that "grief is a difficult thing" and that "it comes in waves," adding that there have been times when he's had to pull his car over while driving because he's been "so upset" following Heche's death.

"This shock that she's gone now — someone that you really loved and really knew very, very well... [It's] impossible to get over quickly," he said.

As for how he and 13-year-old Atlas are coping with the loss, he told PEOPLE, "Atlas has taken up tennis so he plays like two to three hours a day, and I think that's creating a real nice balance." He added that Atlas "has really good friends. So keeping these things carefully in balance, that's how we're getting through grief."

Notably missing from the event was Heche's son Homer Laffoon, whom she shared with ex Coley Laffoon.

At the event, Duffy signed copies of the memoir for fans on behalf of Heche. There were also some farewell messages read.

Actor Alec Baldwin appeared in a tribute video during the evening. In it, he recalled when he and Heche costarred in the 2004 Broadway revival of Twentieth Century. "Anne was of course very bold and very adventurous," he said.

"She was brave," he added. "And she was funny, and she's so many things. But all that aside — all the anecdotes of working and so forth — she was kind. She would reach out to me in tough times I've had or wonderful times I've had, and I would hear from her intermittently but always, 'How are you?' And nothing attached. There was nothing transactional about Anne's love, at least in my case."

The book reading comes five months after the 53-year-old Emmy Award-winning actress was involved in a devastating car crash on Aug. 5.

The actress remained in a coma for nearly a week before she was declared legally dead in the state of California on Aug. 11. Her heart continued to beat until Aug. 14 in order to ensure her organs could be donated in accordance with her wishes.

"Today we lost a bright light, a kind and most joyful soul, a loving mother, and a loyal friend," a rep for the star told PEOPLE in a statement at the time. "Anne will be deeply missed but she lives on through her beautiful sons, her iconic body of work, and her passionate advocacy. Her bravery for always standing in her truth, spreading her message of love and acceptance, will continue to have a lasting impact."

In the months following her death, Heche's older son Homer and her ex James became entangled in a legal back-and-forth. Homer has since been named general administrator of her estate.

Heche had been writing Call Me Anne, her follow-up to 2001's Call Me Crazy, for months leading up to her death.

The book consists of "personal anecdotes of her rise to fame: how Harrison Ford became her on-set mentor, her relationship with Ellen DeGeneres, her encounter with Harvey Weinstein, her history of childhood sexual abuse, her relationship with God, her journey to love herself," according to its synopsis.

Details of the memoir were first released in September by the Associated Press, which published an excerpt ahead of the book's scheduled release date.

Earlier this month, Heche's son Homer spoke about the book and announced the "special" Barnes & Noble event in a post on his mother's Instagram account.

"I have a responsibility to share with her community what she was working on and how excited she would have been to tell you herself," he wrote, in part. "The book is the product of mom's further efforts to share her story and to help others where she could. Call Me Anne is the result and I know she was excited to share with the world."

"So, mom, here I am sharing it with the community you created, may it flourish and take on a life of its own, as you would have wanted," he added. "I know mom would want to see everyone's smiling face as she read an excerpt and signed copies."

In addition to Call Me Anne, Heche had completed several projects before her death. The actress had a role in What Remains opposite Kellan Lutz and Cress Williams, and filmed The Idol alongside The Weeknd and Lily-Rose Depp. She also appeared in Lifetime's film, Girl in Room 13, which premiered in September.

Heche is also expected to appear in the upcoming projects, Supercell, Full Ride, Frankie Meets Jack, Chasing Nightmares and Wildfire: The Legend of the Cherokee Ghost Horse.

Call Me Anne is now available for purchase.