Even though this would have been one of the rare romcom manga where the harem ending truly would have been the easiest way to a happy ending, it seemed pretty clear that such an ending wasn't going to happen. Honestly, it feels like everyone that's been reading from the beginning should be able to predict how this is going to conclude.
Also, polygamy is illegal for meaningful reasons. Because in real life, shit like the scenario in this series virtually never happens. In practice, it's almost always based around significant power disparities between the man and the women and even between the women. Those disparities are often based around things like social caste and economic class (and sometimes race, ethnicity, and religion, as well). Some degree of exploitation almost always comes with the territory.