You don't need to get a promise ring at 13. They can get really expensive easily, and I don't know many 13 year olds that can drop $100+ on a promise ring. Not only that, but you don't need to be discussing marriage at 13. A promise ring basically means "I promise to marry you someday."
I understand your feelings for him. But a promise ring is a mutual thing... you know like when he loves you back and wants a ring too. Either way don't push it or rush it. Let the relationship run its course and if it leads to a promise ring then let love be love. <3