Ignoring the romance of Buddie (something I never thought I'd say), the song Brother by Kodaline fits them so much. Even platonically, they're all in for each other.
And when you're in the trenches
And you're under fire I will cover you
When Eddie was shot? Buck literally was willing to risk getting potentially shot to protect Eddie.
If I was dying on my knees
You would be the one to rescue me
And if you were drowned at sea
I'd give you my lungs so you could breathe
The well, the tsunami, Eddie's breakdown, Buck DYING and Eddie who was also potentially injured immediately running up. AND EDDIE BEING SHOT.
Oh brother, we'll go deeper than the ink
Beneath the skin of our tattoos
Though we don't share the same blood
You're my brother and I love you that's the truth
Eddie and Buck basically have access to each other's houses like it's no one's business. Eddie and Buck whenever they have issues, going to each other for comfort and advice. Eddie and Buck, who know things about each other before everyone else does. Eddie and Buck, literally LEGALLY co parenting Chris?
And if we hit on troubled water
I'll be the one to keep you warm and safe
And we'll be carrying each other
Until we say goodbye on our dying day
The tsunami, AGAIN. This is technically not Eddie, but Buck did everything he could to find and keep Chris safe. Chris, the person who means the most in Eddie's life. The person that Buck knows if anything happens, Eddie wouldn't know how to cope with life anymore.
"You can have my back any day." "Yeah, or you know, you could have mine."
"Buck, there's nobody in this world i trust with my son more than you."
"But no one will ever fight for my son as hard as you. That is what I want for him."