Maze Runner question

So all in all I really liked the book series but disliked the ending.

I liked that they came along the maze where they starteed again but then it only got worse.
They escaped trough the falling apart building and there a dozens of people dying. But in the hectic there are no consequences so its all "nah who cares". Then out of nowhere Teresa dies. I had to go back to that part because first I completly overread the tragedy of it with all the hunderts of other people dying.

I get that its a sign of loyalty to Thomas and maybe love. But it does just feel cheap. Like the author really wanted to finish he books fast and quality does not matter.
Her deathw as random and useless and never gets worked up later. They just forget about it. Was it too hard for the author to find a way out of Thomas likes 2 girls situations?
Thomas don't have to decide which of the 2 he likes more and if he can forgive Teresa (that he is so unforgiving and narrow minded is my biggest character critic of thomas anyway) if shes just killed of at the finish line.