He was forced into the marriage. He couldn't leave the position of queen empty after his first wife died so he ended up in a political marriage with her. Also male heirs are also preferred so i think that also had something to do with it. If you consider the fact that some of the nobles are still trying to nag him to marry their daughters so that he can have a male heir. Granted they do think that Abigail is infertile but in reality it's just because they never had sex. anyways......[spoiler warning] blanche ends up taking the throne so yay her.

Does anyone knows the reasons for the prince to choose to marry the fl in the first place??