What is yearning? Yearning is wanting something just out of reach β the ache of almost, the reach that never quite closes. It's not heartbreak, because heartbreak means you had it and lost it. Yearning is worse: you never got it at all.
Which is exactly Fall Out Boy's whole bit. Nobody tugs the soul like a band that turns bro, you're not getting the guy into a four-minute love song. That's the pull β the lyrics don't just describe wanting, they make you feel the wanting, and then leave you sitting in it. And what you're sitting in, if we're being honest, is a situationship.
A situationship is the relationship that refuses to admit it's a relationship. All the feelings, none of the labels, zero of the closure. You're together enough to get hurt but not enough to call it anything β ouch. The not-knowing is its own kind of anxiety. So when the yearning in these songs lands a little too hard, that's why "Fourth of July" (one of my favorite songs) is more than just a mood disorder with a bassline.
Let's look at the first verse:
I'll be as honest as you'll let me
I miss your early morning company
If you get me
You are my favorite what if
You are my best I'll never know