Let You Down Lyrics Meaning

I can imagine that the whole song is about NF and his relationship with his Dad... A kind of concilliatory text..
but probably mostly from his own point of view...now that he is older and wiser, he looks back and realizes that he too was a tough kid at times... as most kids are as teens for example and that his Dad probably tried his best to be a good Dad..at a time that was also tough for his Dad...

He sings in a harsh tone "Yeah, I guess I'm a disappointment..." This is NF saying all the things that need to be said as a young man rebelling at everything that he thinks makes him a failure so that he can get rid of all his resentment for what happened to his family and the way he saw things when he younger... parents' divorce, teen life with Dad and Mother's suicide etc...

Then, the "older, more reasonable and understanding voice of the refrain:
It's his older and wiser self talking... "I wish that I could say I'm proud... sorry that I let you down..." He realizes that he also screwed up along the way and though he wanted to make his Dad proud, also made some wrong choices in his life...

So, on the one hand he feels disadvantaged and is missing a lot of what he feels his Dad should have given him in terms of love and support and on the other hand he knows that it also wasn't easy for his Dad and feels that he let him down as well...

So I am thinking that maybe this song is a concilliatory gesture to his Dad... on the one hand.. making him responsible for how he turned out but at the same time reaching out to him for forgiveness for the things he also did wrong...