Why does Cam agree to return to the Otherworld with Dawn in the novel, Fairy Tale?

Cam loves Morgan, but when he arrives on the balcony at the Green Toad he hears Morgan confess that she loves Pip. At that moment, Dawn causes vines to wrap around Pip's neck, and Cam agrees to go to Otherworld if she spares Pip. After healing Pip, Cam assures Morgan that he will always love her but this is how things are supposed to be, and then he enters the portal to Otherworld