This manga kind of lost its way in the middle, but dang, all of the lingering readers who care enough to comment are real jerks. Lol.
You can be disappointed at the ending, that's a normal reaction, but you're hella overreacting.
Anyway, my opinion: the manga got back on track in this last arc. Though still meandered, and I think I skipped one or two chapters of confusing action? But these last 5-6 chapters have been pretty solid. Beautiful. A good explanation of the world and of Nike's worldview (you haters did read the title of this story and the first arc, right? Your cynicism is baffling).
I think, if Nike and Livi are going to end up together again, it's going to be at the end of Livi's life. Having made the world a better place, he's going to end up in that world along with the others who were vaguely mentioned alongside past protectors. And they will be happy then.