It’s kind of crazy to me how much Tommy erases everything else in Buck’s mind. Buck is honestly obsessed with him. I mean in the first episode where they meet Buck has just saved Bobby, a man he himself has said is like a father to him, from certain death and instead of rushing to insist he get checked over or hovering to make sure he’s okay (like Buck usually does), he’s lagging behind to make eyes at Tommy. 7x04 is then all about how Buck is thinking about Tommy all time. He’s talking to everyone about Tommy, he’s trying to get invited to karaoke and basketball games to see him, and when Eddie doesn’t take the hint Buck finds a way to show up where Tommy will be anyway. When he’s at Maddie’s wedding after someone else he loved almost died, he’s glued to his phone wondering when Tommy will arrive.
When they break up he’s even more obsessed, thinking about him so often he has to take up a new hobby and talking to anyone who will listen about how much he misses him. And in 8x11, we see the true mind eraser powers of Tommy. Buck is down bad about Eddie moving to Texas, he’s been talking nonstop about Eddie to Ravi all night and then Tommy shows up and it’s like “Eddie who?” Ravi took one look down the bar and thought “thank god, the only person who could get Buck to stop thinking about Eddie is here.” Tommy sits down and all thoughts of Eddie are erased. Tommy is like “Eddie moved” and Buck is like “yeah but it’s whatever, anyway let’s talk about you.”
They go back to Eddie’s house, where Buck hasn’t even started to move in yet because he hasn’t wanted to think about Eddie being gone, and suddenly Eddie leaving is no longer a thought in his mind, all he can think about is getting into Tommy’s pants. He wakes up the next morning to find that Tommy has already done some unpacking, and instead of freaking out about how that means Eddie isn’t coming back, he’s angling for a good morning kiss. Tommy brings up “the competition” and Buck is like “who?” because he’s forgotten every other person in the world exists except the man in front of him. Tommy brings up his jealousy about Eddie and Buck’s brain can’t even comprehend it, like why would he be into Eddie when Tommy is right there.
Later when he’s talking to Maddie about it, Buck once again is only thinking about Tommy. He isn’t phased by the talk of Eddie, quick to say “I’m not in love with him,” and instead spends the conversation talking about what Tommy said, and how Tommy acted. The conversation ends perfectly with Buck saying I should call him and Maddie assuming Buck is talking about Eddie, meanwhile Eddie is already out of sight and out of mind for Buck and he’s back to thinking about Tommy again. When Maddie assumes he means he’s going to call Eddie, Buck is like “Eddie? Why would we be talking about Eddie, I’m obviously talking about Tommy, why would we be talking about anyone else?” I mean that’s crazy, your ex and your sister both ask you if you’re in love with your best friend, while you’re still grieving the fact that he moved to a different state and you’re like “who cares about him, fuck that, I want to talk about Tommy.” You could even argue that Buck is Tommy-pilled in the two part lab storyline where his whole team is locked in a building with a deadly virus and the US military is planing to leave them there to die and Buck’s like “I think this is a good time to call my ex-boyfriend.” Iconic behavior.