Some seem to forget that Irvine is the only one of the orphans that never lost his memory of his life with the orphans, because he never used GFs, until Squall joined them. So, he remembers everything about the past events, about Ellone, etc. He brings this to their attention at Trabia Garden. This could also be the reason why Irvine found it so hard to shoot Edea in the assassination mission. .