Bono resisted offers from across Europe to move to Saudi Arabia.
He told the club's website: "I had some family problems during my last season in Seville, I didn't feel well from a psychological point of view, I wasn't me anymore.
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"I had to draw on my strength and all my experience, but I couldn't because I wasn't emotionally able to continue staying here. I needed a change for my health mental.
"You can't stay in one place knowing you can't be there. In Seville I had very little private life. Train, pick up the dog, take a nap and think about training the next day.
"When I saw that I no longer had the energy to continue giving everything for this club, the opportunity to leave arose and I left."