Invisible by Hunter Hayes

Invisible is a song is about tomorrow that you'll see a better day, that you're not alone, and you're not invisible. It's about people going through hard times and bullying. People will always say things about you and leave you out. One day, it will come to an end and the pain will be gone.

"Someday you'll look back on all these days and all this pain is gonna be invisible."
I think this line means that no matter how hard things get, you can't give up because once you get through it, you'll look back and it'll be like it wasn't even there. It will be invisible.