Dragon

You were secretly a young dragon in a magical disguise. However, The light of a full moon disrupts transfiguration magic revealing creatures for what they truly are. Why else do you think werewolves have to transform on the full moon. If you stayed with Lyra tonight you would burst out of your human form and into the 8ft tall 10ft long young green dragon that you were.

In the house that you were going to share together, there was enough room to curl up and be your true self, even a garden where you could stretch your wings. Until then the only way you could show her was at your family's house. Your parents had a large house and a massive garden where they could sunbathe as their true 20ft long 10ft high gigantic forms.

Safely home and in your room you transformed and coiled around your hoard of books, video games and nerdy collectables. Modern treasure was a lot less shiny and cold. You couldn't wait to show Lyra the real you, knowing she would understand. Out of all the things you had, she was the one you treasured the most and coming from a dragon that meant a lot.