The Italian eventually joined Sunderland in a permanent transfer this summer after rejecting a move to the Stadium of Light last year, and he has now revealed he wasted time by not making the move sooner.
"I wasted too much time - not because I wanted to waste it, or deserved to waste it, I just wasted it," he said.
"That's why I came back to a place where I have been loved, and still feel the love from the supporters."
Borini was left out of Liverpool's pre-season tour of the Far East and Australia, and the forward admitted having to train on his own was the trigger that led to his departure from Anfield.
"It was really upsetting to train on my own," he said.
"It was the killer that led me to leave Liverpool. I always gave everything for the club, and I showed that on the pitch and in training.
"Everyone knows within that club that I did everything and never complained."
When then asked why he had turned down a move to Sunderland last summer, Borini said: "It was a case of a situation which wasn't under my control because of many people around me.
"I couldn't make the right decision and I didn't have the solution under my control.
"When you can't control your future you can't be blamed for something that didn't happen.
"Every player wants to play Champions League football, but, as I said, I couldn't make that decision because I was never put in a place to make that decision."
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