Harry was having a rough day, Voldemort tried to kill him, he got into a fight with Malfoy, said somethings he sould not have, got into a fight with Malfoy. The list can on and on. his day was really turned around when, he and Malfoy, got stuck in the past.
He was falling for you.
Now he understood why they called it 'falling' in love. Like falling off a broomstick, it was happening very quickly and the ground was rushing up to meet him, before he had a chance to react or cast a spell to protect himself. The collision would be inevitable and nobody knew how much it could hurt. There was no slowing down.