The former attacking midfielder was not able to secure a regular spot in Barca's starting XI as he featured just 36 times for the Spanish giants and was loaned out to Stuttgart, Birmingham and Wolfsburg before his contract was terminated by mutual consent.
"Many years later and I still think about it," Hleb said on Arsenal's In Lockdown podcast. "I don't understand. To this day I still don't understand what happened or why I made the decision.
"Of course, Barcelona in that moment was the best team in the world but I was really happy at Arsenal at the time. I had friends, I enjoyed the coach, I was playing for one of the best teams, the fans, the stadium, everything! The fantastic championship, the Premier League, everything!
"Why I left, I don't understand. Barca, of course, were the best team at the time and everybody wants something to try but really I was 100 per cent happy at Arsenal.
"I cried when I talked to Arsene [Wenger]. We talked in the holiday before I left and he told me he wanted to keep me and I was important. I cried. I didn't know what to do in that moment.
"Of course, Barca is a fantastic team. I won titles and everything but I didn't play as much as I did at Arsenal. This is only my mistake because at the time, a lot of things happened in my private life. I started very nervously [at Barcelona]. Always aggressive. It was only my mistake.
"This is not a situation where Guardiola didn't trust me or something like that. No, this is only my mistake. At Arsenal I was happy, you know? When you're happy in the team, you need to stay.
“Of course [I still think about my career]. When you're young you think you have so many years but it's really like one moment. It's really quick. My children now ask me about [my career] and you explain your emotions and it's nice, it's very nice.”