The Love Story star made the confession during his testimony in a Los Angeles court on Wednesday (11Dec13) as part of his long-running legal battle with officials from the University of Texas over the ownership of the Warhol artwork.
O'Neal took the valuable piece from Fawcett's home following her death in 2009, claiming it was one of two he had commissioned the iconic artist to paint, while college bosses allege the actress left the silkscreen to them in her will.
Taking the stand on Wednesday, the 72 year old revealed the painting helped him to feel close to Fawcett.
He told the court, "I talk to it. I talk to her. It's her presence. Her presence in my life. In our son's life. We lost her. I don't want to lose that, too."
O'Neal, who is father to Fawcett's only child, son Redmond, also vowed never to sell the portrait, valued at $12 million (£8 million), if he wins the case, adding, "I plan to keep it in our family as long as there is a family."
The civil trial continues.