What are you talking about? If anything it took way too damn long for him to reveal as her childhood friend since Ayame would never figure it out by herself. The story itself never felt like it was going to be that long considering the premise and that her mission was supposedly to kill him like 10 chapters ago.
Not saying it's bad. We finally are at the conflict Ayame is supposed to face: her family of criminals that raised her as a child soldier or the guy she liked as a kid and is now the head of a criminal organization. There are no good guys in this story and that makes it interesting.