"There's always those questions of 'Why didn't he talk to us? Or 'Why didn't he do anything?'"
The family had never discussed depression or suicide. They had never even thought about it, he said, let alone sought help from an organisation like Lifeline.
In the years since Michael's death, Herlihy feels that things have got worse, not better.
National suicide statistics have risen to more than 600 a year. A day before speaking to the Herald, Herlihy's friend's son, 18, also died in a suspected suicide.
The problem is particularly bad in rural areas, where suicide rates are relatively high and mental health care is often stretched or non-existent.
"We're just one family out of 600," Herlihy said.
"You think, bloody hell, someone else is going through what we had to go through.
"To have somebody, your own son, your own brother - you think it's never going to happen to you, but it did happen to us."
Bereft and looking for a way to respond, he and wife Pat have thrown their energy into fundraising for suicide awareness and prevention organisations.
The family has held 24-hour "shearathons" at their home in Whangamomona, eastern Taranaki. Their efforts have raised $70,000 for Lifeline and local charities.
The alarming suicide statistics make Herlihy even more determined to get people talking about the issue.
"I can't tell you exactly how we're going to save a person's life but it's getting pretty tragic when there's 600 people a year [dying].
"We're doing our best to make people talk about it. I think that's the story . If you're worried about somebody, don't leave them alone.
"Go and play golf, or go fishing, or go hunting or a coffee or a beer or something. Because in our case we didn't have a clue at all."
If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call police immediately on 111.
Or if you need to talk to someone else:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youthline: 0800 376 633
• Need to talk? Free call or text 1737 (available 24/7)
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• Samaritans 0800 726 666
• Rural Support Trust: 0800 787 254.