This was very confusing the first time I read it, but then after reading it again I had my own understanding of it. So here it is:
Obviously the Prince was the chosen one by the Virgin, to remember her when she sleeps and watch all the sins the Virgin couldn't bare to watch. When she sleeps and is not looking at everyone, they awake at night and remember who they really are. I'm not entirely sure how Helga remembers, but it's probably because she, and her mother, sinned when Virgin was still awake. Therefore, their hair turns black, signifying adultery, or something like that.
Master of the Hand, MH, was a man who loved Helga's mother, or possibly just another black haired woman, and actually slept with her. As it was said, his hair use to be blonde but had turn darker due to their sins. So he blames himself for killing Helga's mother because she was executed for it--- SO this makes one wonder who Helga's father is... Hmmmmmm...... Either way Helga and MH falls for each other, because she reminds him of his past lover. Anyhow, I loved the way the author use this trying-to-remember-forgotten love theme to bring a strong angst to the manga, very heart wrenching! (Excluding the [maybe] incest thing.)
As for the Prince, I mistaken he was gay cause I thought Master of the Sin [MS] was a guy, but no she was girl. You can tell he loves her (not sure if in the form of lover, best friend, or sister), but there's obviously guilt or sadness involved when he sees how crazy MS becomes when the virgin is sleeping. That's why he had decided to reject her love, obviously after having slept with her when the bell had tolled before. I'm pretty sure their feelings are mutual, so that was why he didn't give his love to the Virgin, but when he wanted to save Helga from execution, he sacrificed his love and ran towards her,. That's why the curse on the town was lifted, and I believe the Virgin wanted to love and be loved in return. That's why she called Mayor, her "Prince."
In the end, a villager mentioned that the island was possibly surrounded my monsters and I believe this is because the Virgin was one, but I'm not 100% sure as well. Helga and MA became Major of that island with the help of Eda, and the Prince and MS, AKA Johanna, met up and probably traveled together. Everyone had forgotten about the Virgins and that's why the Prince questioned why he cried when he saw the doll, because it was like the Virgin had become nonexistent, like it mentioned in the manga. 'If it's not remembered, it pretty much doesn't exist.'