Hes talking about love I mean the first line my head is an empty box, have you ever had that feeling like your so mind is so empty but your heart is plenty full the second verse he talks about some girl and he likes everything she does then the last chorus he says "Baby please Open your heart And catch my disease" hes saying love me back, hes so in love with her and saying if she wouldnt be so stubborn she might love him too.