Chapter 8. The part in italics wherein Draco flashbacks to the night Harry first made love to him (Draco bottoming first) and after that, Harry asked if Draco would like to top him. Draco said yes, mostly because he has never topped before in his past relationships (reason being his previous boyfriends were selfish jerks who had never cared much about what Draco wanted). If it's any consolation, Harry's clearly the dominant one in their relationship and as you read, you'd find that Draco prefers bottoming.