Dean McDermott "inflicted a lot of damage and pain" on Tori Spelling.
The 'Chopped Canada' host admitted on his Instagram announcement in June that their 18-year marriage was over was posted while he was under the influence and his struggles with alcohol and drugs slowly destroyed their relationship.
He told DailyMail.com "All Tori's ever done to this day is want me to be happy and healthy and I inflicted a lot of damage and pain on that woman.
'I'm taking accountability for that today. And it's the biggest amend that I'm ever going to have to make...
"It's going to be living the rest of my life making amends because I took something that was really beautiful and I just tore it down year after year, day after day."
McDermott - who has Liam, 16, Stella, 15, Hattie, 12, Finn, 11, and six-year-old Beau with Spelling - claimed he and the 'Beverly Hills 90210' star had been living mainly as "roommates" and hadn't shared a bedroom since 2017, and though he is now dating Lily Calo, he will always love his estranged wife.
Speaking from rehab, he said: "Life happens. It's tough having kids. It's tough living in this town, tough, having financial problems. It's just really tough. I'm not making excuses. I certainly had my hand in it in the dissolution of the relationship. But yeah, hasn't been easy. Nothing in life is easy."
The 56-year-old star - who also has 25-year-old son Jack with first wife Mary Jo Eustace - blamed "Hollywood" and "all the s*** people gave us" as one of the reasons for the breakdown of their marriage, but he wants to take "accountability" for his own behaviour.
He said: "Alcohol made me feel good enough. I started feeling good enough until it got to a point where it didn't – it ended up in isolation.
"It ended up with me drinking a fifth of tequila every night, seven days a week, and a handful of narcos [prescription meds] by myself with a beautiful family in the other room.
"That's what it led to and that's what led to the brokenness and to what happened between me and Tori.
"I couldn't do it anymore. I couldn't live that life anymore. I was tired of the anger and the yelling."