The song is about how he has found a girl who is beautiful. He can't keep her outta of his head and just the thought of this girl is making him smile like a idiot and hes saying how he smiles and is so happy with the thought of her that he feels like hes going crazy for her.
It kinda reminds me of the time I met my Girlfriend I can relate to this song because I'm crazy for her. She makes me smile, laugh, and feel loved when ever I'm in a terrible mood. The thought of her makes me go crazy, just how Dylan is feeling in this song.
Shes just so beautiful that I'm going crazy for her.