Clarke quit in 2015 after his 115th and final Test of the Ashes series against England and said he didn't allow himself to grieve at the time.
Hughes, who played 26 Tests, died from bleeding on the brain in November 2014 after being hit on the neck by a rising ball while batting in a domestic match at the Sydney Cricket Ground.
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"I shouldn't have played another game. My career should have stopped then. It was too hard for me," Clarke told The Weekly Review on Thursday. "It took me a lot longer to grieve his loss than it should have, or that I would have liked.”
He added: "I didn't allow myself to grieve at the time because I had responsibility to his family, firstly, but then also as Australia's cricket captain to my teammates and getting us back out onto the field."
Clarke, who was a pallbearer at Hughes' funeral and delivered an emotional eulogy to his "little brother", said that after he died, he felt fear for the first time while playing cricket.
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Clarke toured the West Indies in June 2015, which he said was a mistake.
"Going to the West Indies was probably the worst tour of my life in regards to how emotional I was," he said. "I was there on my own. Unfortunately Kyly (his wife) couldn't come because she was pregnant and we weren't comfortable with her flying. I had six weeks in the West Indies ... whatever we had on as a team during the day I would go back to my room every night and just cry myself to sleep."
He said there were days when the pain of missing Hughes was still raw. "I still have days regularly where it's heart-breaking. It's still raw ... the emotion and pain is still there."
Since his retirement, Clarke has commentated on cricket for Australia's Nine Network. He also runs his own cricket academy among other business interests.
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