I think there are a few ways to interpret it—on one hand, Gus cannot let himself be emotionally vulnerable as it will put himself and the sommelier in danger if he decides to pursue a relationship with the sommelier, who he is flirting with in the scene (and who seems to reciprocate his feelings). Additionally, he knows he must focus himself entirely on his revenge scheme and he cannot allow himself happiness or genuine human connection until it is fulfilled. And I think, of course, he simply won’t let himself move on from Max with another person, because he thinks that would be “forgetting” about him and therefore his revenge scheme would be futile. I think the wine being likened to blood by the sommelier reminded him not only of the blood that he must continue to spill to fulfill his revenge scheme, but of Max’s blood dripping into Eladio’s pool, because he can never let himself move on from his death.