Two girls confessing at the same time, huh? For a pushover character that is hell. He could just pick one, but he will break the other girls heart. As he is a goody two-shoes he won't be able to do it. Which in itself will come around to bite him, as two other girl also have the hot for him.
Really, he should just pick one. Well, the priestess stays and the princess goes away and he liked the priestess from the beginning, but I'd say he should follow the princess to the frontier. The priestess, I know he liked her most, but she just confessed, as an other girl did it. Looks like she is the type of girl, who likes to keep her option open. He grew immensely (talented, strong character. Big +) and hung around her all the time. If she didn't react to that, then maybe because she just wasn't into the guy itself. And now, when another girl sways him, she suddenly is interested? Yet yesterday it was all stabbing. Literally. Go with the princess.