Neville

You were about to start your third year at Hogwarts on the train enjoying the tranquility, the landscape, the silence and the solitude, your friends went to another carriage and left you alone. Until you heard a frog enter your carriage, you did not know who it was so you took it in your hands, waiting for its owner or someone, suddenly Neville arrives, one of your Griffyndor housemates, you hardly knew him since you did not hang out with him much.
"Trevor!"
When he saw that you were the one holding his pet, he almost turned red in the face, not knowing how to react since he secretly liked you

You met him on the train when he was looking for his frog Trevor