The 25-year-old joined Inter from Porto last summer, but failed to make an impact at the San Siro.
“When I was at Inter, I wasn’t feeling very confident, I wasn’t playing well and I wasn’t happy,” he told the official Chelsea website.
“I already feel more confident here at Chelsea. It has brought the joy back for me, which I didn’t have at Inter.
“I lost my will and motivation, and that is important for a footballer, to be happy, which I am now because I got my confidence back.”
He added: “Every championship in the world has its own mentality and way of playing.
“Everybody likes to play in the English league. I think this is because it’s a very competitive league – players come here and learn a lot.
“They get stronger, physically and psychologically – they have to in order to play here, and you have to keep this level high.
“Everybody wants to play here. It helps you improve and become stronger.”