The 25-year-old handed in a transfer request in August after the Catalan club had a bid for him rejected, but the Reds paid no attention to his demands and turned down a further two offers with owners Fenway Sports Group publicly stating he was not for sale.
Coutinho has subsequently been successfully reintegrated into the team, having missed the start of the season with a back problem, and, despite sitting out the last three matches with an adductor injury, he is set to feature in Tuesday's friendly against England.
"I'm playing in one of the biggest leagues in the world," he told Sky Sports.
"I'm always happy. But now it's important to concentrate on the national team. At the moment I am very happy with my life.
"Every day, I work harder than before to improve myself and become a better all-around footballer."
Liverpool will also be boosted by the news Coutinho has declared himself fully fit again.
"Unfortunately, I could not play for Liverpool in the past three games because of injury," he added.
"Now I feel 100 per cent fit, I have recovered and I am in a good shape to be available for the game against England.
"I never want to miss any Brazil games. I am honored to wear this shirt whenever I can."