So actually beast the dumbass , soft loving demon eater was actually born he hasn't always apart of darkest and darkest mare but unluckily most demon eaters are born with a whole soul but for beast he has a rare problem that some demon eaters have its where they only have half a soul 

       When a demon eater has half a  soul when they find a mate they take part of there mates soul and gives there mate there half soul to share and keep later on if the demon eater is happy and in love with there mate there half soul  is reborn and shares there mates soul 

Beast: *holds half of a glowing heart* Eh good luck finding a mate beast .......AGH IM TALKIN TO MYSElF