OH MY GOD I CRACKED IT.
RHYS ISN'T AGAINST AZRIEL AND ELAIN, HE'S TERRIFIED THAT WHAT HAPPENED TO MOR WILL HAPPEN TO ELAIN.
WHEN MOR WAS ENGAGED TO ERIS, BUT SLEPT WITH CASSIAN SHE WAS TORTURED.
HE'S SCARED THAT IF ELAIN GETS WITH AZRIEL, WHILE MATED TO LUCIEN, SHE'LL BE HURT.