Each Act, he will get 1 main girl, next act, he say goodbye to that girl and move to the next main girl
Keep repeating it.
What I hate the most is "All girl will be replaced in the next act". Author always finds some stupid ideal to make them part way.
I think that Author is afraid that people will get bored if 1 girl appears too much, so he keep replacing them. Best girl, good girl, best Waifu, everyone will be replaced.
Like iPhone, when Apple releases higher version, they stop support the outdate version.
Pirate girl is the only one who can meet him a second time (appear in 2 seperate acts), before leaving for good (I doubt she will ever appear again, SO SAD).