The 70-year-old actor - who has four children, daughter Tatum, and sons Griffin and Patrick from previous relationships, and son Redmond with Farrah - was devastated when his long-term partner lost her battle with the disease in June 2009 and thinks his fractured relationship with his children caused her undue stress, triggering the illness as her life was otherwise healthy.
He said: "What bothers me the most is that there was turmoil during my love affair with Farrah. A lot of it caused by my family, by my kids. All of them. Particularly Tatum. That I just think that if she had never met us, would she still be alive today?
"Because nobody knows what causes cancer, do they really? And she didn't smoke. And she didn't drink. She exercised every day. And she believed in her good health. And then we came along. The four of us. And gradually she got weaker. I don't know. I think it's highly possible. I wasn't able to straighten out the mess that we were in and we sucked her in."
Ryan is still struggling to come to terms with Farrah's death and revealed he often has to talk Redmond - who has a history of substance abuse and has spent time in jail on drugs charges - out of wanting to commit suicide.
In an interview on CNN show 'Piers Morgan Tonight', he revealed: "You know, Farrah was a very strong presence in my life. So strong. She permeated my mind and my being. She still does.
"I hear songs that we loved and it stabs me and brings her back. And I'm OK with that. I had somebody that I loved.
"And I have a son who struggles with his life because he's tempted to join her, and he's 26. He's tempted to go because he misses her so much. And he feels he shamed himself so much. And it's tricky.
"It's crazy. I say to him that's not what she wants. She wants you to have a wonderful life. Live it for her. She doesn't want you to join her. And he agrees, but I'm not sure he does. He just says he agrees."