I would just like to know how they ended up together.
This is what many readers would have wanted, unfortunately, for a variety of reasons, the ending is lacking from this point of view.
There must be an effort on the readers' side to appreciate the meaning of the ending and many, even if they have understood the reasons for the choice, have not yet appreciated it.
I among them
The point I would like to emphasize is the one mentioned by KingLil-Leem, a significant reason why he liked her. The reasons given by the manga are scarce and almost contradictory. Deeper meanings can be found, but they give little color to the choice.
Apart from the now infamous issue of the rushed ending, what was missing was an understandable ending for everyone (I don't criticize who was chosen, but how she was chosen)
I think that they could make 5 separate endings with him marrying each sister like whoever he ends up with, in the movie will be the canon. But they could release 4 OVAs each being like 30 minutes with a story about him and the other sister. I doubt this will happen but if they did, I think it would make a lot of people happy.