Louis Tomlinson Says It's Impossibly Difficult to Cope Without Liam Payne

Louis Tomlinson is reliving the heartbreak again -- a year after Liam Payne’s tragic death, he admits the pain of losing him still feels impossible to bear.

In a new interview, Louis admitted the band’s 15th anniversary earlier this year felt painfully empty without Liam ... but said they all knew celebrating was just as important -- if not more -- in Liam’s honor.

Louis told Rolling Stone it still feels unfair and frustrating that Liam wasn’t there with them ... confessing he’s still carrying all those raw, heavy feelings every day.

Louis -- who’s already endured the heartbreak of losing both his mother and sister -- admitted he naively thought he understood grief for his age, and Liam’s death might somehow feel less crushing. But it hit differently, he said ... because he’d never lost a friend before.

It was an emotional sit-down, with Louis also hailing Liam as the most seasoned of the bunch before 1D formed ... someone they all quietly looked up to, even if their pride as young men kept them from saying it back then.