Brown Song for Whitney Houston 'Don't Let Me Die

An emotional Brown -- sporting sunglasses and leather pants -- performed the song on "The Tonight Show with Jay Leno" ... featuring the lyrics, "I didn’t realize that every breath I took was from you ... You were my air.

Brown also sings,"I guess I messed up pretty bad ... I didn’t know who you were ... I didn’t know what we had. Now I’m stuck living in the past ... trying to get the pieces back ... but I guess now you’re gone."

Brown is releasing the song on his new album, which drops in June ... just 4 months after Whitney died.