Tuiasosopo said his motives were pure; he never tried to make money off their relationship. "I just wanted to help him become better," he said.
The charade became difficult to maintain, and he tried to end it several times.
"There are many times where Manti and Lennay had broken up. But something would bring them back together, whether it was something going on in his life or Lennay's life, in this case in my life," Tuiasosopo said.
He added: "I wanted to end it because after everything I had gone through I wanted to move on with my life. Me, Ronaiah, I had to just start living and let this go."
Finally, after learning that Te'o had Skyped with four women -- including two of his former girlfriends -- Tuiasosopo said he essentially killed off Lennay, having her die of leukemia.
"I was just trying to do everything to end it because I knew that, no matter what, you know, it just wasn't right -- and it was never going to be."
In Friday's segment, Tuiasosopo apologized to all those he hurt, including Te'o, Teo's family and his own family. "I can't express how sorry I am," he said. "The truth is I hurt every day for the decisions I have made."