Gojo Satoru's last words to Geto Suguru were expressing their close friendship. The exact phrasing is not explicitly stated in the given contexts, but they all agree that Gojo referred to Geto as his "best friend" and "one and only" [1] [2] [3] [5] [6] [7] [8]. There are theories that Gojo may have also said "I love you," but not in a romantic sense, but as a unique and sole friend [8]. The manga's creator, Gege Akutami, has not yet revealed the precise words, but it's clear that Gojo's message to Geto conveyed a deep, heartfelt bond between them [4].