Because of the fight between him and pain the confession was pushed to the back of naruto's mind. So technically it took him at least a few years before realizing and returning her feelings.
OMG, That picture with him and Himawari thou!!! It's so sweet!! Fan girl mode activated (and I don't even fan girl) *screams internally in blissful delight*. It's sooooooooo adorable I love it!!! I swear Gaara-sama, as much I love you (and I'm low [high] key glad you're not into anyone in the series, I think you'd make an AWESOME father! Uggh. Gaara-sama, you're the greatest. Marry me already, damn it.