They could have been happy together if they just talked it out
Well, maybe. The situation is definitely far from ordinary, and it is difficult to guess how everything would have happened if the characters behaved differently.
However, they did what they did, I just...
SPOILERS!
... I just hope that Leo was able to overcome his obsession with Chase, because the saddest fact for me was that he was left alone. He simply refused to move on with the others, and although he survived, leaving him behind was extremely painful.
I also thought that everything could be settled, maybe that's why my first ending was tragic...