When he asked you out.
Ashton took you to a ice skating rink. During while you two were skating he asked you out!
You two were sitting on his couch, playing pokèmon. After you beat him, he did nothing but stare at you. He then grabbed your hand and rubbed it. He also asked you out!
You and Luke were hanging out. You guys were playing on your guitars during a song he wrote he said "if only (Y/N) would go out with me." You guys then started dating.
Since you and Calum have been friends forever, he knows exactly what you like! He took you on a long walk on the beach and he asked you out at dawn.