She said while Kahu died from injuries caused by a head-on crash with a truck on the Rotokawa straights, Hepa was physically uninjured.
"But the emotional pain for him is why he is where he is now," Ms Morehu said.
She said Hepa spent the weekend leading up to his death with his cousins at their marae where his body was later found by family members.
"The night before he died, he was so happy.
"They played cards, they sung songs, played silly buggers with his aunties, uncles, cousins," she said.
"One minute he was happy, the next he was gone.
"That's all I remember at that time," Ms Morehu said.
"I had conversations with him, a lot earlier than when he took his life, asking whether he felt suicidal because there was a lot of deaths happening in Kawerau.
"And I got frightened because I don't know how many there were - the signs professionals say to look for - from the 20 [signs] he had two - does that make him suicidal, do I do this or that?
"Sometimes you're stuffed if you do and you're stuffed if you don't."
Ms Morehu said that out of all her six children he had been the most honest and up-front when she confronted him.
"He said, 'Yeah, I think about killing myself, I think about killing myself every day. Why should I still be stuck here and feel like this when Kahu is gone?'"
The Tree of Life: My journey with grief is Ms Morehu's emotional account and voice of a whanau directly impacted by suicide. She credited her extended whanau and iwi for the support they gave her and her family.
"There's always a feeling of someone missing [at home], that feeling of incompletion, [it's] just empty. I couldn't function, I didn't see why I should get up the next morning, I didn't want to. I told my darling, 'This sucks, it's too sore and it just doesn't go away'. There's no sunshine, no understanding, it's all anger and dark, no one knows."
It was through the help of a Facebook page for parents and family who had lost a loved one to suicide that Ms Morehu was able to share her pain.
"From there I felt a lot more courage to get up in the morning. But now I understand my son's grief, I understand his pain because I too have felt it. I'm lucky I'm here to tell my story and their story. I forgive him and I love him more than I did when he was born."
Also speaking at the launch was Ms Morehu's husband, Taupe Pou Poasa, her father and kaumatua, Te Ariki Morehu, and Toni Redgrave, who shared her story of the loss of her younger brother.
Ms Morehu also spoke at Pounamunui Marae, Okere Falls, yesterday before speaking in Reporoa, Taupo and Turangi this week.
Her book has been supported by Te Runanga o Ngati Pikiao and Ms Morehu's employer, Te Wananga o Aoteroa. For more information go to www.treeoflife.org.nz
Where to get help:
Youth services: 06 3555 906
Youthline: 0800 376 633
Kidsline: 0800 543 754 (4pm to 6pm weekdays)
Whatsup: 0800 942 8787 (noon to midnight)
Depression helpline: 0800 111 757 (24-hour service)
Rainbow Youth: 09 376 4155
If it is an emergency and you feel like you or someone else is at risk, call 111
