@Rezef
Basically since Ines chose Carcel to marry that made it difficult for the CP to have Ines as his wife. Previously married women aren't allowed to marry royalty. So the only way he can have her is to make her his mistress. However, the CP can't make her a mistress if he doesn't already have a wife. That's why the CP has a fiance and that's why he's tormenting Carcel/trying to get rid of him. So he can make Ines a widow/divorcee and force her to be his mistress. (Please correct me if I'm wrong on anything.)
Basically since Ines chose Carcel to marry that made it difficult for the CP to have Ines as his wife. Previously married women aren't allowed to marry royalty. So the only way he can have her is to make her his mistress. However, the CP can't make her a mistress if he doesn't already have a wife. That's why the CP has a fiance and that's why he's tormenting Carcel/trying to get rid of him. So he can make Ines a widow/divorcee and force her to be his mistress. (Please correct me if I'm wrong on anything.)
love you my a** 
