Why is everyone acting like her and Gilbert are already a couple? Especially since, as some other commentors have mentioned, he did trick her into signing a very unfair contract. You can't exactly build a loving, trusting relationship with something who would swindle you in a heartbeat if they think there's something to gain. There's just not much chemistry between the two leads, at all. He acts superficially nice but really hasn't taken any concrete action that qualifies as truly kind. A well written story could easily reveal him to be a sociopath.
Gilbert probably would be an excellent King, mostly because he has an utterly ruthless nature that would make the sort of tough decisions leaders have to. The very traits that make me dislike him are ones that would make him the sort of hard man Kingdoms need.