after rewatching it like a million times in a row just now, i think the argument in 8x09 might be one of my favorite buddie scenes, actually. it just displays so blatantly how well eddie knows buck, the good and the bad, and how much he loves him even through hurt and anger.
eddie is mad, he is so mad, and he lays out some of buck's biggest character flaws, not to hurt buck, but to get them communicating. he doesn't want buck not to be pissed at him or suppress how he feels, he just wants buck to be honest about it. and then buck admits he's having trouble with eddie leaving and eddie no hesitation confirms he feels the same, and accidentally exposes what's been in his head, that he's choosing between buck and chris, that this is a choice that hurts him to make. because he loves buck.
and eddie is still mad but here buck makes his sweeping gesture, you don't have to choose, he is your son and you need to be with him. and eddie's emotions are all over the place he doesn't have time to process a thing he's just slapped in the face with how much buck loves him, how much buck loves chris.
the whole scene illustrates so clearly, through it all eddie sees buck, loves him to his core, no matter how frustrating he gets the love and knowing doesn't waver. and, of course, buck doesn't let him forget, he loves him right back.