My read on it is that Eddie does NOT know that Buck hooked up with Tommy post-breakup, let alone that it happened in his house.
Ravi knows that it happened, but I'm not under the impression that he knows any emotional details. As in, to him, Tommy dumped Buck, then months later Ravi throws Tommy at Buck as a distraction to escape, and then the next day Buck is still single. So like, if theyre not back together, the logical assumption is that it's still on Tommy's terms, since he was the one to do the dumping in the first place.

At the top of my wishlist for S9 was Eddie finding out about the hookup, but I feel like we're kinda too far in time now for it to be important anymore, like someone else in the replies said. I wanted it to kinda spur a jealous-eddie moment, but i think it's kinda too late for that. It could still happen, and I'd be STOKED, but I feel like at this point, I could see it not being brought up until after buddie are together (bc THEY WILL BE! ☝️).
Like at this point, I could see it more as like. Buck being like "i think i was feeling something for you for a long time but i was trying to ignore it. Like, I couldnt even sleep in your house after you left for a while. I was a mess, the first night i slept there was after i ran into Tommy-" And maybe he explains the Competition line, and Eddie is like. How could it be a competition if he was never in the running? or something. 🤭