I am unsure who will end up as main girl. They are pointing us one way while teasing the other, all while constantly switching the two. I'd say this would be like any typical mauhua, but he wasn't raised with nor really know anything about the one he "loves". So I feel they are having it up in the air for that reason.
I, personally, would go with the princess. As she is the one who has helped him the most (if that's what he's using as a basis for his affection).