It's embarrassing how worked up he was.. it's not like he was asking for your hand in marriage. Just a simple question; Will you be my Valentine? He didn't know why but having you say yes was so very important to him. He's been planning this for weeks, learning your favorite flowers and candy. But he just felt so embarrassed. Especially with his love letter! So he did the only sensible thing and left it in your locker. XD