The endings of Raymond Briggs’ The Snowman and The Snowman and the Snowdog are sad. The dog doesn’t understand, which seems all the more sad.
But long-term, it’s even sadder. The boy can build the same snowman every year, as evidenced by The Snowman and the Snowdog, but one year, he’ll be too old to want to build snowmen and walk in the air with them, and his snowman will never be again.